You have to find the average of 38 and 42 (witch is 40) and then set it to a ratio of 40:100 multiply both sides by 8.5 and we get 340
Here's the solution,
the volume of the given figure is :
=》

volume of pyramid :
=》

=》

=》

=》

volume of pyramid = 40 cm³
now, volume of rectangular prism :
=》

=》

=》

volume of rectangular prism = 40 cm³
volume of composite figure = 40 + 40
=》80 cm³
Answer:
Its the second option. 742.5