There are two ways to solve this. The longer way is to use those equations to calculate numbers for total distance.
The easier way is to find the area under the graph. That's right, AREA UNDER VELOCITY-TIME graph is the TOTAL DISTANCE travelled!
it's a shortcut.
Let's split up the area into a triangle and rectangle:
Triangle = 0.5(4-0)(10-0) = 20 m
Rectangle = (6-4)(10-0) = 20 m
Total distance = 40 m!