Calculus Word Problem - No Solution! ? :O

The question was on our exam today, and several of us are dumbfounded after it. We knew how to solve this question, and we went about our business, and it turned out badly. I took it home and compared it to my method before, and I had the correct method, the numbers are correct, but the numbers work out badly when we get to a certain point, because it gives a negative instead of a positive like before.

Anyways here's the question. Please solve and show us your solution :(

There is an island 60 meters from land. 150 meters down shore is an ice cream store. A man on the island wants to get ice cream. He can swim at 3m/s and run on land at 5m/s . TO what point down shore should he swim to minimize the time to get to his beloved ice cream? (Must be Ben and Jerry's?)

Thanks guys... We called the distance down shore, x, and the distance he ran, 150-x . And the distance swam in the lake is (x^2 + 60^2)^(1/2)

Let me know if oyu are going to answer this :P Wet my tastebuds. get my excited for something cause we're down and out about this.