520 CD's because of the 9 months and we add 30 time 9 we erase the 0 and multiply the 3 with the 9 it will be 27 right we add the zero because the originla number is 30
Let length=x, witdth=x-9
Perimeter=130
2 length+2 width=130
2x+2(x-9)=130
2x+2x-18=130
4x=130+18
4x=148
X=37 cm
Length=37cm; width=37-9=28cm
Hope this can help.
Cross multiplication, 3(9+x) = 63
27+3x = 63
3x = 63-27 = 36
x=36/3=12
