It depends upon whether or not the wall is load bearing. If load bearing, the distance between standard studs is nominally 16 inches. If not load bearing, it can be 24 inches. There may be complications at the ends of the wall and doors and windows will also increase the number of 2x4's that are needed. A good rule of thumb is to figure one per foot. So in your case that would be 16.
Every 16" and you'd need 25
It's unlikely you would use many 2X4s on a deck. The joists (under the decking) are usually 2X6 or larger. The larger the joist, the fewer you need, because you can space them further apart. The decking is made of 1X6s nailed or screwed to the top of the joists, and running perpendicular to the joists or at an angle to the joists. The amount of decking you need depends on whether you intend to make a pattern (herringbone) or a typical deck. The railing might include 2X4s as the top rail, but the support posts are usually 4X4s, and in between those, you usually use small stock to add the decorative posts/slats.
It depends on the size of the bricks and their orientation.
The answer will depend on the size of the bricks.
9 if the studs are on 16" center and 7 if on 24"
144/8 = 18
25
28
Standard studs are spaced 16" apart. 30 feet times 12 inches = 360 inches. 360 inches divided by 16 inches = 22.5. If you are measuring left to right, the right-side stud from the frame becomes the last one. Depending on how you will compensate for the extra 8" at the end, you will need 21 or 22 2x4s.
56
Every 16" and you'd need 25
It's unlikely you would use many 2X4s on a deck. The joists (under the decking) are usually 2X6 or larger. The larger the joist, the fewer you need, because you can space them further apart. The decking is made of 1X6s nailed or screwed to the top of the joists, and running perpendicular to the joists or at an angle to the joists. The amount of decking you need depends on whether you intend to make a pattern (herringbone) or a typical deck. The railing might include 2X4s as the top rail, but the support posts are usually 4X4s, and in between those, you usually use small stock to add the decorative posts/slats.
It depends on the size of the bricks and their orientation.
The answer will depend on the size of the bricks.
you would need about 99 people to build a castle.
There are different sizes of brick. You will need to know how many bricks are in a square foot, including the mortar joint.
9 if the studs are on 16" center and 7 if on 24"