What is the average flight speed of an unladen swallow?

the average flight speed of the unladen swallow is 31 to 40 miles per hour

Dont mind the sign until fourth step

First step: find divisibles of 90
1,2,3,5,6,9,10,15,18,30,45,90

Second step:find the pairs
1*90,2*45,3*30,5*18,6*15,9*10

Third step: find which one has a difference of 5
None of them is (expand this question more so i can help you)