Answer:
a: 
b: 5
c: 8
Step-by-step explanation:
<em>Explanation for a: Making the equations</em>
Assuming h is the amount of half-page ads and f is the amount of full page ads, we can create the equations
since the total cost will be 800$, and we have a total of 13 ads.
<em>Explanation for b: Solving for h</em>
We can now solve for one of the variables using elimination. Let’s multiply the expression
by -75.

Great! Now let’s add the equations.

Adding these equations, we get

Divide both sides by -35, and we get
.
<em>Explanation for c: Solving for f</em>
We can now substitute h inside the equation
.

Hope this helped!