Answer :

This can be solved using a ratio. The ratio is: 13/20=x/60 this would then become 20x= 780  divide both sides by 20 and you get x=39. the answer is 39
LouEarley
It can go in a more simple way.

20 goes into 60 3 times, this 3 being the multiplier.

13 x 3 = 39
_
20 x 3 = 60

39:60 homes on a street with 60 homes have personal computers.
:D