设 原来的长为X,宽为Y,那么有
(X+6.5)Y-XY=136.5
(Y+6.5)X-XY=234
解出X、Y,解XY的值就行
XY+6.5Y-XY=136.5 Y=21
XY+6.5X-XY=234 X=36
XY=21*36=756