So i tried to this question and got f(x) = 1 + x
upper estimate = 9
lower estimate = 6
wondering if i'm on the right path. thx!
thanks for the graph. i think i got it! the lower limit represents, in this case, the area of the red rectange. the upper limit represents the the area of the triangle + rectange multiplied by 2 since we take the upper value of x therefore = 4x3 = 12