(a)
we are given
the price of apple suddenly up by $0.75
Let's assume original price be 'p'
we are given
Sam bought 3 pounds of apple at the new price total is $5.88
so, new price = old price +0.75
price of 3 apples 
we are given that price is 5.88
so, we get equation as
.......Answer
(b)
Since, original price is p
so, we have to solve for p
so, original price is $1.21 per pound........Answer
9/100 = x/90
Cross multiply to get 810 = 100x
Divide both sides by 100 to get x = 81 inches
C would be your answer and here is how you would solve the problem.
Cross Multiply by 'x - 5'
Hence
y(x - 5) = 4 -3x
xy - 5y = 4 - 3x
Move all the terms containing an 'x' to one side of the equals and all the others to the opposite side.
xy + 3x = 4 + 5y
Factor out 'x'
x(y + 3) = 4 + 5y
'Cross' divide by 'y + 3'
x = ( 4 + 5y) / (y + 3 )
'x' is now the subject.
13.01 < 13.1 because there is a 0 in the tenths place in 13.01 and there is a 1 in the tenths place in 13.1
