Question

a patrat - b patrat =45
a+b=15
5a-5b=?

Answer 1

a²-b²=(a-b)(a+b)=45
15(a-b)=45, a-b=3
5a-5a=5(a-b)=5x3=15

Answer 2

a²-b²=45
a²-b²=(a-b)(a+b)
(a-b)(a+b)=45
a+b=15
15(a-b)=45
a-b=45÷15
a-b=3

5a-5b=?
5(a-b)=5×3=15