Idon’t understand how to multiply polynomials

3x^4 +7x^2 -20

Step-by-step explanation:

To find how tall the building is, multiply how high each story is by the number of stories

height = (x^2+4) * (3x^2-5)

FOIL

first x^2 *3x^2 = 3x^4

outer -5x^2

inner 4*3x^2 = 12x^2

last -5*4 = -20

Add them together

3x^4 -5x^2 +12x^2 -20

3x^4 +7x^2 -20

1. 8

2. 9

3. 20

4. 3

5. 17

6. 2.2

7. 11.25

8. 1

9. 14

10. 2

step-by-step explanation:

thats the first half

the answer is 99.