In patterns, we look at one example to try to "guess" the pattern. Then we apply our "guess" into the next example to check if it works.

Looking at top left pyramid,
36.8, 8, 4.6 is related by 36.8 ÷ 8 = 4.6
We test this on the top right pyramid,
0.15, 5, 0.03 -> 0.15 ÷ 5 = 0.03
So this relationship is correct.

Applying it on the bottom pyramid
A, 3, 20.9 -> A ÷ 3 = 20.9
A = 20.9 × 3 = 62.7

Looking again at top left pyramid
18.4, 13.8, 4.6 is related by 18.4 - 13.8 = 4.6
Testing on top right pyramid
0.05, 0.02, 0.03 -> 0.05 - 0.02 = 0.03
We find our guess to be true.

Applying it on bottom pyramid
31.35, B, 20.9 -> 31.35 - B = 20.9
B = 31.35 - 20.9 = 10.45