750 inc 20%. Net figure before 29%addition

The original plus 20% of the original is 750.

Let x represent the original; then 20% of the original is 20% times x  --->   0.20x

The equation becomes:

     x + 0.20x  =  720

--->   1.20x  =  720

Divide by 1.20:

--->         x  =  600

The original was 600.