the given expression is,
-4x + 3y = 25 ,,,,,,(1)
and
y = 3x + 15
subtitute the value of y in equation (1)
-4x + 3( 3x + 15) = 25
- 4x + 9x + 45 = 25
5x = 25 - 45
x = -20/5
x = -4
put x = -4 in y = 3x + 15
y = 3(-4) + 15
y = -12 + 15
y = 3
thus, the answer is x = - 4 and y = 3