Sagot :
What a delightful little problem !
You said that (4 + x) / (9 - x) = -9
Multiply each side by (9 - x) : (4 + x) = -9 (9 - x)
Eliminate parentheses: 4 + x = -81 + 9x
Add 81 to each side: 85 + x = 9x
Subtract 'x' from each side: 85 = 8x
Divide each side by 8 : 85/8 = x (or 10.625)
You said that (4 + x) / (9 - x) = -9
Multiply each side by (9 - x) : (4 + x) = -9 (9 - x)
Eliminate parentheses: 4 + x = -81 + 9x
Add 81 to each side: 85 + x = 9x
Subtract 'x' from each side: 85 = 8x
Divide each side by 8 : 85/8 = x (or 10.625)
(4+n)/(9-n)=-9
4+n=-9(9-n)
4+n=-81+9n
4+81=9n-n
85=8n
n=85/8=80/8+5/8=10+5/8
4+n=-9(9-n)
4+n=-81+9n
4+81=9n-n
85=8n
n=85/8=80/8+5/8=10+5/8