Part A)
From equation (1) the value of y comes out to be:
y = 4x - 15
Using this value, in equation 2, we get:
5x + 3(4x-15) = 40
5x + 12x - 45 = 40
17x = 85
x = 5
y = 4x - 15
⇒
y = 4(4) - 15
y = 20 - 15
y = 5
Therefore, the solution set to the given equations is (4, 5)
Part B)
The graph of the lines intersect at one point, so they have a unique solution.(First option is correct)