Number of Dell laptops sold by store Q is approximately what percent of the number of the number of laptops (both Dell and Lenovo) sold by store R?

Percent of Dell Laptops sold by store Q = 25%
Total number of Dell Laptops bold by store Q
$$\eqalign{ & = 2400\times\frac{25}{100} \cr & = 600 \cr} $$
Percent of Laptops Dell and Lenovo sold by store R = 35%
Number of Laptops Dell and Lenovo sold by store R
$$\eqalign{ & = 4500\times\frac{35}{100} \cr & = 1575 \cr & \therefore \text{Required Percentage} \cr & = \frac{600}{1575}\times100 \cr & = 38.095 \cr & \approx 38\% \cr} $$