if you bring a number across the = sign it changes it's sign.
-12=p-4
-12+4=p
-8=p
If that doesn't make sense, feel free to message me. Basically, isolate the letter to equal a number.
p4 + 3O2 ---> 2PO3
12 + 5 equals...
-12 (?)
12/3 = 4
25
Add 12 to each side: a = 36 + 12 = 48
If n + 7 = 12, then n = 12 - 7
3x=12 3x/3=12/3 x=4
x=12
-0.5
x=12
8 - 4d = 12-4d = 4d = -1