A company has two electric motors that consume varying amounts of power. The power consumed by each motor is a function of the time (t in minutes) for which it runs. The cost of power (in $) to run one motor is given by the function `C_a(t) = t^2 - 2t + 5`. The cost of running the second motor is given by `C_b(t) = 3t + 2`. Which function gives the total cost of running both motors?