First you can calculate area of the base. In your case the base of the prism is triangle with base 6 cm and height 7cm. Its area is S=h*L/2=6*7/2=7*3=21 cm^2. Then you multiply area of the base by the height of the prism to find its volume V=S*H=21*10=210 cm^3. The answer is 210 cm^3