So it is easiest if we first draw out the triangle and label it.We use an equation called Pythagoras' Theorem. This equation is A^2 + B^2 = C^2So we know the length of side A (3) and side C (6), lets put this into the formula:3^2 + B^2 = 6^29 + B^2 = 36B^2 = 27B = √27B = 5.20 (2DP)