Explanation:
3y=4x+7_equation 1
5y=4x+25_equation 2
multiply equation 1 by 5 an equation 2 by 3
15y=20x+35_equation 3
15y=12x+75_equation 4
subtract equations 4 from equation 3
0=8x-40
40=8x
divide both sides by 8
x=5
substitute x into equation 1
3y=4(5)+7
3y=20+7
3y=27
divide both sides by 3
y=9