A rectangular prism has a base area 56 ft.² and a volume of 840 ft.³ the length of the base is longer than the width if the sum of the length and the width of the base is equal to the height of the pyramid what is the length of the base in feet

The length of the base in feet is 8 ft.

Step-by-step explanation:

The volume V of the rectangular prism is given by

V = l × w × h

But Area, A = l × w

∴ V = A × h

Where A is the base area and h is the height

From the question

A = 56 ft.²  and V = 840 ft.³

∴ 840 ft.³ = 56 ft.² × h

840 ft.³ / 56 ft.² = h

15 ft. = h

∴ h = 15 ft.

Hence, the height of the rectangular prism is 15 ft.

Also, from the question

the sum of the length and the width of the base is equal to the height

i.e l + w = h

where l is the length of the base and w is the width of the base

Then, l + w = 15 (1)

Also, A = l × w

Then, 56 = l × w (2)

From equation (1)

l + w = 15

Then, w = 15 - l (3)

Substitute this into equation (2)

56 = l × w

56 = l × (15-l)

56 = 15l - l²

Then,

l²- 15l + 56 = 0

l² -8l -7l + 56 = 0

l(l - 8) -7(l - 8) = 0

(l - 7)(l - 8) = 0

l - 7 = 0 OR l - 8 = 0

∴ l = 7 OR l = 8

Substitute the values of l into equation (3)

w = 15 - l

when l = 7

w = 15 - 7

w = 8

and when l = 8

w = 15 - 8

w = 7

From the question, the length of the base is longer than the width

∴ l = 8 and w = 7

Hence, the length of the base in feet is 8 ft.

the answer is a if my teacher taught me correct

i think the answer is b