An efficiency study showed that the rate at which the average worker assembles products t hours after starting work can be modeled by the function

f(t) = t²+ 12t+ 15 ,where0 t 4

Determine the number of units the average worker can assemble during the fourth hour that s/he works during a shift.

a)45 units

b)8 units

c)135 units

d)2 units

e)132 units

f)None of the above.