$$ABC$$ is a triangle in which the angles are in the ratio $$3 \colon 4 \colon 5$$. PQR is a triangle in which the angles are in the ratio $$5 \colon 6 \colon 7$$. The difference between the least angle of $$ABC$$ and the least angle of PQR is $$a^\circ$$. Then $$a$$ =

For $$ABC$$, dividing $$180^\circ$$ in the ratio $$3 \colon 4 \colon 5$$ gives parts of $$15^\circ$$ each, so the least angle is $$3 \times 15 = 45^\circ$$. For $$PQR$$, dividing $$180^\circ$$ in the ratio $$5 \colon 6 \colon 7$$ gives parts of $$10^\circ$$ each, so the least angle is $$5 \times 10 = 50^\circ$$. The difference is $$50 - 45 = 5$$, so $$a = 5$$.