A = number of apples
B = number of bananas
C = number of oranges (I would use the letter O, but it looks very similar to the number zero)
A = B - 2 since the number of apples is 2 less than the number of bananas
C = 4*A ... since number of oranges is 4 times that of the number of apples
C = 4*A
C = 4*(B-2) ... plug in A = B-2
C = 4*B-8
A+B+C = total amount of fruit
A+B+C = A+B+4*A .... replaced C with 4*A
A+B+C = (B-2)+B+4*(B-2) ... plug in A = B-2
A+B+C = B-2+B+4*B-8
A+B+C = 6B - 10
The expression 6B-10 represents the total amount of fruit we have. If we know how many bananas there are, then we can compute 6B-10 to find the total amount of fruit (we don't need to know A or C).
Now set each possible answer choice (18,22,26, & 30) equal to 6B-10 and solve for B. The goal is to see which equation leads to a whole number
Set 6B-10 equal to the value from choice A
6B - 10 = 18
6B = 18+10
6B = 28
B = 28/6
B = 4.67
So we cross choice A off the list
Set 6B-10 equal to the value from choice B
6B - 10 = 22
6B = 22+10
6B = 32
B = 32/6
B = 5.33
So we cross choice B off the list
Set 6B-10 equal to the value from choice C
6B - 10 = 26
6B = 26+10
6B = 36
B = 36/6
B = 6
Looks like this is the answer. Let's check D just in case.
Set 6B-10 equal to the value from choice D
6B - 10 = 30
6B = 30+10
6B = 40
B = 40/6
B = 6.67
So we cross choice D off the list
So that's why choice C is the answer.