43. (a) Find the coordinates of the centroid of a triangle whose vertices are: A (−1, 3), B (1, −l) and C (5, 1) (Leave no spaces in your answer.)   44. (b) Use a ruler and a pair of compasses to construct ΔABC in which BC = 4.2 cm, ∠ABC = 60° and AB = 5 cm. Construct a circle of radius 2 cm to touch both the arms of ∠ABC of ΔABC.   45. (c) A shop keeper buys a certain number of books for Rs. 720. If the cost per book was Rs. 5 less, the number of books that could be bought for Rs. 720 would be 2 more. Taking the original cost of each book to be Rs. x, write an equation in x and solve it.