Dear aspirant,

The question asked by you is just a formula based question . The formula is 1/v - 1/u = 1/f.

With the help of this formula you will be able take out what's asked in the question.

Given data :- Focal length = 15 cm, Image position = -17 cm.

So, just put in the formula with the sign.

1/-17 -1/u = 1/15

->1/u=- 1/15 -1/17

1/u = -32/255

u =- 255/32

That's your answer.