How to solve these kinds of problems?
I deffinitly recomment to look at your calculations. But the abbility of cannot rolling tongue is recessive not dominant. And after all look at the Hardy-Weinberg equision p^2 + 2pq + q^2 = 1 (p*p=p^2). Try to extract the root of q^2 and you will get right sollution (because the 0.16 is squareroot).