To solve this, you need to isolate/get the variable "x" by itself in the equation:
3(x - 5) + 7x = 65 Distribute 3 into (x - 5)
(3)x + (3)(-5) + 7x = 65
3x - 15 + 7x = 65 Combine like terms(terms that have the same variable and power/exponent), or combine 3x and 7x
10x - 15 = 65 Add 15 on both sides
10x - 15 + 15 = 65 + 15
10x = 80 Divide 10 on both sides to get "x" by itself
x = 8
PROOF
3(x - 5) + 7x = 65 Substitute/plug in 8 into "x" since x = 8
3(8 - 5) + 7(8) = 65
3(3) + 56 = 65
9 + 56 = 65
65 = 65