Take your pick of the ways shown in the attachment.
f(2.5) means x is equal to 2.5.
Replace x in the equation with 2.5 and solve:
6(2.5) + 1.5 = 15 + 1.5 = 16.5
f(2.5) = 16.5
If you have one per box you got 20 broken in all.
Z-score for 80% to pass = -0.842.

-60.624 = X - 426
X = 426 - 60.624
X = 365
Therefore the required passing score is 365.
Answer:
C, never negative
it can be zero in exactly one occasion