Explanation:
we can substitute book B as B
we can substitute book A as A
using the information above we can create an eqaution
we know B is $15.00 more than 3 times the cost of A
B = 3A + 15.00
we know the sum of the books is $75.00
A + B = 75.00
substitute B with eqaution 1 we will get
A + 3A + 15.00 = 75.00
4A + 15.00 = 75.00
- 15.00 -15.00
4A= 60.00
A = 15.00
which means book A is $15.00