Answer: The missing number is 55
The denominators are 20 and 100. We multiply by 5 to jump from the smaller denominator to the larger.
Do the same for the numerators
11*5 = 55
Or you can solve the proportion below for x
11/20 = x/100
11*100 = 20*x
1100 = 20x
20x = 1100
x = 1100/20
x = 55