A certain organization sells boxes of 32 oranges for $8.00 per box, bo

"If the unit price of each kind of fruit is independent of the kind of box in which it is packed" ---- this is to create unwanted confusion.
Given:
I. boxes of 32 oranges for $8.00 per box
price per orange="a"= 8$/32= (1/4)$ ----- (i)

II. boxes of 20 grapefruit for $7.00 per box
price per grapefruit="b"= 7$/20 ----- (ii)

III. combination boxes of oranges and grapefruit for $8.50 per box
let x be the number of oranges and y be the number of grapefruits in combination box
==> 8.5$=(x*a+y*b) ------ (iii)

IV. each combination box contains twice as many oranges as grapefruit
x=2y ----- (iv)

substituting (i), (ii), and (iv) in (iii) we get (or values of a, b and value of x in terms of y)
8.5$= (1/4)$*2y + (7/20)$*y
or
8.5= (5/20)*2y + (7/20)$*y
or
8.5= (17/20)*y
or y=10
or
number of grapefruits in combination box = 10 = option D