25022

If we represent a circle as “a” a triangle as “b” a square as “c” and a pentagon as “d”.

3c + b = 30
2c + 2b = 28

6c + 2b = 60
2c + 2b = 28
1 – 2
4c = 32
c = 8
b = 6

We can use simultaneous equations to find out what a square is and what a triangle is.

3a + 6 = 18
3a = 12
a = 4

Now we know what a circle is.
8 + 8 + d = 23
d = 7

We can now use a pentagon to find the question mark.

8 + 6 + 7 = 21

The question mark is 21.