Question 210780
You can use any letters of choice.

I will use U and R.

Let U = unrestricted parking spaces 

Let R = spaces reserved for the handicapped

U = 12 + 7R

U + R = 6452

We have a system of linear equations in two variables.

Since we are given U to be 12 + 7R, let's plug that into the other equation and solve for R.

12 + 7R + R = 6452

12 + 8R = 6452

8R = 6452 - 12

8R = 6440

R = 6440/8

R = 805

We just found the spaces reserved for the handicapped.

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We now plug R = 805 into either equation to find U.

I will use U + R = 6452 but you can use the other equation if you so desire.

U + 805 = 6452

U = 6452 - 805

U = 5647

The unrestricted parking spaces is 5647.

The spaces reserved for the handicapped is 805.

Did you follow?  

NOTE: If you add 805 + 5647, you will get the total number of parking spaces, which was given to be 6452.