Answer:
1. 84in³
2. 180cm³
3. 600ft³
4. 360cm³
5. 312cm³
6. 15.6kg
7. 1.95kg
Explanation:
1: V = Bh = (7x3)x4 = 84in³
2: V = Bh = 1/2(8x5) x 9
 = 20 x 9
 = 180cm³
3: V = Bh = 1/2(b1+b2) h x 5
 = 1/2(20+10) 8 x 5
 = 15 x 8 x 5
 = 15 x 40
 = 600ft³
4: V = Bh = 1/2 (4x9) x 20
 = 18 x 20
 = 360cm³
5: Total volume = Volume of rectangular prism + Volume of triangular block
 = (8.5 x 4 x 9) + 1/2(1.5 x 2) x 4
 = 306 + 6
 = 312cm³
6: divide 312cm³ by 20kg/cm³ to get the approx. mass:
 312/20 = 15.6kg
7: first find the volume of the friends Display:
 = (4.25 x 2 x 4.5) + 1/2(0.75 x 1) x 2
 = 38.25 + 0.75
 = 39cm³
Now divide by 20 to find the approx. weight of the friends display:
39/20 = 1.95kg
Have a nice day! :)