A sum of Rs. 600 amounts to Rs. 720 in 4 years by simple interest. What will be its amount if the rate of interest is increased by $2\%$?

Initial parameters: Principal $P=600$, Time $T=4\text{ years}$, Amount $A=720$.Initial Simple Interest ($\text{SI}$) = $720-600=\text{Rs. }120$.When the rate of interest is increased by $2\%$, the extra interest earned over 4 years can be directly calculated on the Principal:
$$\text{Extra Interest}=\frac{P\times \text{Extra Rate}\times T}{100}=\frac{600\times 2\times 4}{100}=6\times 8=\text{Rs. }48$$
$$\text{New Total Amount}=\text{Original Amount}+\text{Extra Interest}=720+48=\text{Rs. }768$$