Let x represent some number
Sum of 3 and twice some number = 3 +2x
Five times the sum of 3 and twice some number: 5(3+2x)
5(3+2x)=70
15+10x=70
Subtract 15 from both sides to have 10x by itself
10x=55
Divide 10 on both sides to get x by itself
x=55/10
x=5.5
Hope this helped