12. What is the sign of the following? Answer "positive," "negative," or "zero." (CONSIDER SLOPE OF TANGENT)

a. f'(2)
c. f'(4)
e. f'(7)
b. f'(x) in the interval (1, 3)
d. f'(x) in the interval (3,6)
f. f'(x) in the interval (6, 9)
g. f'(x) in the interval (9, 12)
Find the interval(s) where the function is increasing and the interval(s) where it is decreasing:
27. h(x):
37. h(x)=
15. f(x) = 3x +5 17. f(x) = 2x²+x+1 21. g(x)= x³ + 3x² +1
1
2x + 3
83. AVERAGE SPEED OF A HIGHWAY VEHICLE The average speed of a vehicle on a stretch of Route 134 between 6 A.M. and 10 A.M. on a
typical weekday is approximated by the function f(t) = 20t-40√t+50 (0 ≤t≤4)
where f(t) is measured in miles per hour and t is measured in hours, with t = 0 corresponding to 6 A.M. Find the interval where fis
increasing and the interval where f is decreasing and interpret your results.