Please help with #84 and #85. Practicing for AP exam.

84. Let f be a differentiable function such that f(1) = x and f'(x) = Vx' +6. What is the value of f (5) ? (A) 11.941 (B) 14.587 (C) 24.672 (D) 27.814 85. People are entering a building at a rate modeled by f (t) people per hour and exiting the building at a rate modeled by g(t) people per hour, where t is measured in hours. The functions f and g are nonnegative and differentiable for all times t. Which of the following inequalities indicates that the rate of change of the number of people in the building is increasing at time t ? (A) f(t) > 0 (B) f' (t) > 0 (C) f (t) - 8(t) > 0 (D) f' (t) - 8' (1) > 0