Below is an instruction that describes a task. Write a response that appropriately completes the request in Swahili. Please answer in Swahili.

### Instruction:
Angela wants to check her math homework answers with her friends, but some of them aren't done yet. Out of 20 problems, Martha has finished 2, Jenna has finished four times the number Martha did minus 2, and Mark has finished half the number Jenna did. If none of the friends worked on any of the same problems, how many problems have no one but Angela finished?

### Response:
 Martha amemaliza maswali 2, hivyo Angela yuko maswali 20 - 2 = <<20-2=18>>18 mbele yake.
Mara nne ya idadi ya maswali aliyomaliza Martha ni 4 x 2 = <<4*2=8>>8.
Hivyo, Jenna amejibu maswali 8 - 2 = <<8-2=6>>6.
Idadi ya maswali aliyomaliza Mark ni 6 / 2 = <<6/2=3>>3.
Jumla ya maswali ambayo Martha, Jenna, na Mark wamejibu ni 2 + 6 + 3 = <<2+6+3=11>>11.
Hivyo, hakuna rafiki yeyote wa Angela aliyemaliza maswali 9 kati ya maswali 20.