Here is how to do the problem:
First, set each of the shapes equal to a variable. So here's how I am going to do it:
circle=y
square=x
triangle=z
x+y=53
2y=36
z+18=45
This means that y=18.
Then, let's plug in y=18 into x+y=53.
x=35
Then, finally, we subtract 18 from 45.
z=27
The circle=18
The square=35
The triangle=27
