@waitmaya A.40cm
To solve it, you need to find the difference in the left to right sides and divide by 2. If you simply find it, it'll mean that there are 2 SpongeBobs.
Generalization math formula
(R-L)or(L-R)×1/2=A.
If you wanna find the Rock Height...
(R+L)or(L+R)×1/2=A.