3+7(6+2x)=157
We move all the characters to the left:
3+7(6+2x)-(157)=0
We add all the numbers and all the variables.
7(2x+6)+3-157=0
We add all the numbers and all the variables.
7(2x+6)-154=0
Multiply
14x+42-154=0
We add all the numbers and all the variables.
14x-112=0
We move all terms containing x to the left side, all other terms to the right side
14x=112
x=112/14
x=8