To find the area of a prism, you calculate the area of the cross-section and multiply that number by the length. The cross-section of this prism is a trapezium, and the formula for this is 
.
Insert your given numbers to find out the area of this prism's cross-section:
Now, multiply 90 by the length, 10cm, to find out the volume of the prism;
90×10=900cm³
Therefore, your answer id the third option.
Insert your given numbers to find out the area of this prism's cross-section:
Now, multiply 90 by the length, 10cm, to find out the volume of the prism;
90×10=900cm³
Therefore, your answer id the third option.