For clarification, < is less than, > is greater than, and then there is =.
A. So you have to take the percent of each number first.
50% of 20 = 0.5 x 20 = 10
40% of 30 = 0.4 x 30 = 12
Then put in the appropriate sign.
10 < 12
B. 75% of 12 = 0.75 x 12 = 9
30% of 20 = 0.3 x 20 = 6
9 > 6