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

### Instruction:
A highway is being extended from its current length of 200 miles up to 650 miles. 50 miles are built on the first day, and three times this amount are built on the second day.  How many miles still need to be added to the highway to finish extending it?

### Response:
 Urefu wa barabara kuu ambao unahitaji kujengwa ni 650 - 200 = <<650-200=450>>450 maili.
Kiasi kilichojengwa siku ya pili ni maili 50 * 3 = <<50*3=150>>150.
Hii inamaanisha kuwa baada ya siku mbili, jumla ya maili 50 + 150 = <<50+150=200>>200 zimejengwa.
Hivyo, bado kuna maili 450 - 200 = <<450-200=250>>250 ambazo zinahitaji kujengwa.