15) First given ratio is 21/10.
For second one we have 50 in denominator. So, multiplying top and bottom on 21/10 by 5, we get
21*5/10*5 = 105/50.
Let us find other numbers of missing ratios.
21*6/10*6 = 126/60
21*8/10*8 = 168/80.
16) Given : 4/11
4*2/11*2 = 8/22
4*8/11*8 = 32/88
4*4/11*4 = 16/44
17) Given: 76/92
76÷2 / 92÷2 = 38/46
38÷2 / 46÷2 = 19/23
19*3/23*3 = 57/69
18) Given :42/49
First we would divide top and bottom by 42/49 to reduce in simplest fracion, we get
42÷7 / 49÷7 = 6/7
6*5/7*5 = 30/35
6*6/7*6 = 36/42.