Finding the energy stored in a 5uF capacitor
Remember that an integral is just the area under the curve. So you can use basic geometry to find these integrals.

So, at 1.4 ms, for example, you just have 

$$\int_{-\infty}^{1.4 \rm{ms}}i(t)dt = \frac{1}{2}(1.4\ \rm{ms})(10.5\ \rm{mA}) = 7.35\ \rm{\mu{}C}$$

using the formula for area under a triangle. (And assuming \$Q(t=0)\$ is 0)