A hobby shop sells 4 times as many model of airplanes than model helicopters the total number of model is 35

let's call airplanes "a" and helicopters "h".

The total number of models is 35. This means that a+h=35

4 times as many model airplanes as model helicopters. This means a=4h.

we can substitute this into the previous equation:

4h+h=35

5h=35

dividing by 5:

h=7

so he has 7 helicopters and 4*7=28 airplanes