It appears as if 12cm is half the length of the side so we can assume that the total length of one side is 24cm.
The area of a square is given by the equation
where s is the length of the side.

A=576
The area of this square is 576cm2.
Hope this helps!
If you're asking for the model for the second problem (I didn't see any unsolved), here it is!
The distributive property: a(b - c) = ab - ac
27 - 18r = 9·3 - 9·2r = 9(3 - 2r)
1836 you just multiply 34 x 54