99
9n + 18 = 81 9n = 63 n = 7
108
few errors in your title: 2 plus 4 = 6 6 plus 9 = 15 10 plus 25 = 35 18 + 81 = 99
The factors of 18 are 1,2,3,6,9, and 18. The factors of 81 are 1,3,9,27, and 81.
81% = 81/100
18 + 81 = 99
Gee, I don't know. Let's check it out. If it is, then 18 x 18 = 81 . 18 x 18 = 324 Nope. 18 x 18 is not 81, so 18 is not a square root of 81.
18/81 = 2/9 (divide top and bottom by the hcf of 18 & 81 = 9)
The reciprocal of 1.8 is 1/1.8, which equals 0.5555... .
4.5
81 multiplied by 18 is 1,458.
81 x 81 = 6561