Do you mean 7.5 divided into 21.60? If you do, you can get rid of the decimal point by multiplying both numbers by 100 which moves the decimal point two places to the right. So we have 750 divided into 2160:
2160/750. Remove the zeroes from the end of top and bottom: 216/75. We can divide top and bottom by 3: 72/25=2²²⁄₂₅. We need to convert ²²⁄₂₅ into a decimal: we can do this by multiplying the fraction by 100: ²²⁄₂₅×100=22×4=88 hundredths=0.88, so the full answer is 2.88.
If you meant 7.5 divided by 21.60 we have 750/2160=75/216=25/72. We can simplify this by dividing 25 by 9 then 8 because 8×9=72. 25/8=3.125, then we divide by 9: 3.125/9=0.347222...