Find the value of

*l*in the frustrum above-
**A.**

5cm -
**B.**

6cm -
**C.**

7cm -
**D.**

8cm

##### Correct Answer: Option A

##### Explanation

ΔABE and ΔACD are similar

∴ | x |
| |||

x+4 |

6x = 3(x+4)

6x = 3x + 12

3x = 12

x = 4

In ΔACD; L^{2} = (4+4)^{2} + 6^{2}

= 8^{2} + 6^{2}

= 64 + 36

= 100L =

√ 100

= 10cm

In ABE, AE^{2} = 4^{2} + 3^{2}

= 16 + 9

= 25

AE = 5cm

∴L = 10 – 5

= 5cm