I don't think it's a linear equation between the distance to the sun and year length. Also, if the sun is much smaller/lighter than ours (and ours is fairly big), then the planet can stay in orbit with a slower speed.
I agree that, if you want to be precise on this, some number crunch would be needed. Given the laws of gravity, the mass of of the sun, and the distance from the planet to the sun, and assuming a mostly circular orbit, the time it takes for the planet to orbit the sun is determined to a good approximation. (If it's too slow it would fly toward the sun. If it's too fast it would fly away.)