Using the slope and one point format.
Slope, m = 6, Point = (1, 4), x₁ = 1, y₁ = 4
y - y₁ = m(x - x₁)
y - 4 = 6(x - 1)
So the equation is y - 4 = 6(x - 1), option B
Hope this explains it.
I think C but probably try to find something to back it up
All you gotta do is divide the pound by the cost
112.50 divided by 15 is 7.5= 7.50 so 7.50 times 10 is $75.00 so answer is $75.00