A=(a+b/2)h is the formula hope that helps
Let's represent the numbers by : x, x+1, x+2, x+3
x+x+1+x+2+x+3=40 The third number in the sequence is x+2
4x+6=40 8.5+2=10.5
4x+6-6=40-6 Therefore the third number in the sequence is
4x=34 10.5
4x/4=34/4
x=8.5
180x feet^3
this is the answer because volume is lwh so 15 x 12 x x is 180x the labeled is 180x ft.^3