Question 317940
The outside edge is 60 & 40.
The inside edge is (60-2*1.5) & (40-2*1.5).
Thus we have the surface area of:
a=60*40-(60-3)(40-3)
a=2,400-(57*37)
a=2,400-2,109=291 ft^2.
The depth is 30 in. or 2.5 ft. 
291*2.5=727.5 ft^3 is the total volume of cement required.