Step-by-step explanation:
As ratio of desktops to laptops=3:4
Take no. of desktops= 3x
Take no. of Laptops=4x
Total no. of desktops+ Total no. of laptops = Total no. of computers
3x+4x=70
7x=70
x=10
Hence, the total no, of desktops= 3x
Hence, Total no. of desktops= 3×10
=30 desktops