Your subject title says that this is from the Kaplan
math book. Could post the official explanation? I agree with you that Statement 1 is sufficient, and that the answer should be A.
Using algebra, what I came up with indicated the cost differences would be based entirely off amount of labor required.
The generic equation for this is c = pl + hr = pl + 36h
c = cost
p = price per liter
l = liters of paint required
h = hours required to paint
r = labor rate, which is stated as 36
(for simplicity I'll use capital letters for the variables of paint A, and lower case for the variables of paint B)
If P is the price per liter of paint A, and p is the price per liter of paint B, then:
P/p = 4/3
Meanwhile, the ratio liters of paint A needed to the liters of paint B needed are (this is the inverse of the coverage of A to the coverage of B):
L/l = 3/4
So, the pl portion of the equation c = pl + 36h is equal for either kind of paint.
We know that the ratio of hours required painting with paint A to hours painting with paint B is:
H/h = 3/4
Thus, we are left with the following cost equations:
Cost of paint A: C = PL + 36H
Cost of paint B: c = PL + 48H
where P, L, and H are for both equations stated in terms for paint A.