To evaluate a function at a specific x value, you simply need to substitute all occurences of x with that specific value.
So, starting from [tex] f(x) = (3x+7)^2 [/tex], substitute every occurrence of x with 1 to compute
[tex] f(1) = (3\cdot 1 + 7)^2 = (3+7)^2 = 10^2 = 100 [/tex]
