Question

What is the value of a in the equation 5a – 10b = 45, when b = 3?

Answer 1

To get the answer we have to substitute b=3 and solve it.
5a-10b=45
5a-10*3=45
5a-30=45         /+30  add 30 both sides
5a-30+30=45+30
5a=75              /:5    divide both sides by 5
5a:5=75:5
a=15 - its the answer

Answer 2

$5a-10(3)=45 \\ 5a-30=45 \\ 5a=75 \\ a=15$