What is the difference between number of laptops (both Dell and Lenovo) sold by store Q and total number of Lenovo laptops sold by store R and S together?

Percent of Laptops Dell and Lenovo sold by store Q = 23%
Number of Laptops Dell and Lenovo sold by store Q
$$\eqalign{ & = 4500\times\frac{23}{100} \cr & = 45\times23 \cr & = 1035 \cr} $$
Percent of Laptops Dell and Lenovo sold by R and S together
  = 35% + 11%
  = 46%
Now, total number of Laptops Lenovo and Dell sold by R and S together
$$\eqalign{ & = 4500\times\frac{46}{100} \cr & = 2070 \cr} $$
Percent of Dell Laptops sold by R and S together
  = 30% + 9%
  = 39%
Number of Dell Laptops sold by R and S together
$$\eqalign{ & = 2400\times\frac{39}{100} \cr & = 936 \cr} $$
Number of Lenovo Laptops = 2070 - 936 = 1134
Required difference
  = 1134 - 1035
  = 99