What number is missing? explanation please

1 (first circle), 4 (second circle)

Step-by-step explanation:

In the first circle if you multiply the central number, 5, with any number in the top-half of the circle, you get the number opposite it in the bottom half of the circle. For example, if you multiply 5 with 3, you get 15, which is directly opposite to 3 in the circle.

In the second circle, if you multiply the central number, 3, with any number in the bottom-half of the circle, you get the number opposite it in the top-half of the circle. For example, if you multiply 3 with 5, you get 15, which is directly opposite 5 in the circle.

Let me know if you don't understand.

Hope this helps!

a - base

b - exponent

so,