The function looks something like
And since the definite integral is the area under the curve, you can find it by finding A1, A2, A3, A4 and adding them together:
A_{total}=A_1+A_2+A_3+A_4
Now, they're all trapezium's and the area of a trapezium is
\frac{h}{2}(a+b)
(Where h is the height, a is...