You multiply it with the same number you use for the denominator. in this case 3/4 and 7/10 you find the LCM of the denominator is 20 so for 4 to become 20 you multiply by 5 then for the numerator 3 also multiply by 5, so you get 15/20 its the same also with 7/10, you multiply both the numerator and the denominator by 2 and get 14/20 hope it help... :)
