x/5-y/4=15/10, x/2-y/3=5/6 solve by substitution

Question

I do not understand how to solve this problem by substitution.

Answer 1

line 1...(x/5) -(y/4)=(15/10)...2x-2.5y=15

line 2...(x/2) -(y/3) =(5/6)...3x -2y=5...2y=3x-5...y=1.5x-2.5

plug this intu line 1...2x-2.5*(1.5x-2.5)=15

2x -3.75x+6.25=15

-1.75x=15-6.25...=8.75

x=-8.75/1.75...x=-5

y=1.5x-2.5...1.5*(-5) -2.5...-7.5 -2.5...-10

Answer 2

x/5-y/4=15/10 ··· Eq.1, x/2-y/3=5/6 ···Eq.2   Multiply both sides of Eq.1 by 20, and Eq.2 by 6, getting

4x-5y=30 ··· Eq.3, 3x-2y=5 ··· Eq.4   Multiply both sides of Eq.3 by 2, and  Eq.4 by 5, getting

8x-10y=60 ··· Eq.5, 15x-10y=25 ··· Eq.6   From Eq.5, we have:

10y=8x-60   Substitute this into Eq.6, getting

15x-(8x-60)=25   Remove the brackets, 15x-8x+60=25, so 7x=-35   Divide both sides by 7.  

We have: x=-5   Substitute x=-5 into Eq.3, 4(-5)-5y=30, so -5y=50   Divide both sides by -5.

We have: y=-10  

The answer is: x=-5 and y=-10