Step-by-step explanation:
-3x - 7y = -63
-(3x + 7y) = -63
3x + 7y = -63/-1
3x + 7y = 63
Value of x
3x + 7y = 63
3x = 63 - 7y
x = (63 - 7y)/3
Value of y
3x + 7y = 63
7y = 63 - 3x
y = (63 - 3x)/7
The sum of the measures of angles in all quadrangles is 360 °. Therefore:

Turn the percentage into a decimal
7.5%=0.075
.075x=7.38
Divide both sides by .075 to isolate x
x=98.4

Notice that

which means the series is divergent. So if this is one of those "select all that apply" questions, then both (c) and (j) are the only choices that do.