Aconstruction worker is building solid concrete stairs. how many cubic feet of concrete are needed to make stairs?

The picture in the attached figure

we know that
To know the amount of cubic feet needed, calculate the volume of the stair
we can divide the stair into three rectangular prisms

Volume rectangular prism N 1=6*9*1.5----> 81 ft³
Volume rectangular prism N 2=6*6*1.5----> 54 ft³
Volume rectangular prism N 3=6*3*1.5----> 27 ft³

total volume=81+54+27-----> 162 ft³

the answer is
162 ft³ of concrete are needed