You collect a total of $75 in donations from three people. The three donations are in the ratio 4 : 4 : 7.
4/[4+4+7] =4/15 x 70 =$20 one donation
Same for ratio of 4 -The second donation =$20
7/[4+4+7] = 7/15 x 70 =$35 the third donation.