5. The duration of a construction activity was estimated to be in the range [2, 6] days with a most likely duration of 4 days. A construction engineer used the

following symmetric density function to model the duration: f_{x}(x)=\left\{\begin{array}{ll} b x, & \text { for } 2 \leq x \leq 4 \\ a-b x, & \text { for } 4 \leq x \leq 6 \end{array}\right. Determine the necessary constants a and b to have a legitimate desity function. Graph both the density and cumulative functions.