Answer:
last year 100 boys and 60 girls, for a total of 160.
this year, 120 boys and 75 girls, for a total of 195.
35 more than 160 is a 21.8% increase
5: 5, 10,15,20,25 ( Not sure if 5 counts as one, if it does not, then 30 is another multiple.)
70a + 55b = 905
a + b = 14
55a + 55b = 770
(70a-55a) + (55b-55b) = 905 - 770
15a = 135
a = 9
a + b = 14
9 + b = 14
b = 5