The four subdivisions are 1 -> 1.5, 1.5 -> 2, 2 -> 2.5 and 2.5 -> 3.

So you calculate the value of the function at each of the 5 points at the boundaries of these intervals and apply the rule for finding the area of a trapezoid:

A = x (y_1 + y_2) / 2

for each trapezoid, then add them all up.