4x+y=25
x-3y=16
substitute the value of y into the equation by moving 4x (from the first equation) to the right side
y=25-4x
substitute the given value of y into the equation x-3y=16
x-3(25-4x)=16
x-75+12x=16 (add 75 to both sides of the equation)
13x=91 (divide by 13 both sides of the equation)
x=7
y=25-4x=25-(4×7)=25-28=-3
answer: x=7, y=-3