The first thing you should do for this case is to know the volume of tangerines, which in this case is given by:
V = (4/3) * (pi) * ((d / 2) ^ 3)
The diameter of the tangerines is 2 inches
V = (4/3) * (pi) * ((2/2) ^ 3) = 4.19 in ^ 3
Then, you must know by a rule of three how much in^3 of tangerines you need to have 7oz of juice.
1.4 ---> 7
7 ---> x
Clearing x we have:
x = (7 / 1.4) * (7) = 35 in ^ 3
It takes 35 in3 of tangerines to make 7 ounces of juice.
Then, the number of tangerines will be:
n = (35) / (4.19) = 8.35
nearest whole number:
n = 9
answer
you need 9 tangerines to make a 7 ounce glass of juice