a)
A = 1/3 - 1/3 * 4 / 7
A = 1/3 - 4/21
A = 1x 7/3 x 7 - 4/21
A = 7/21 - 4/21
A = 3/21
A = 3 x 1/3 x 7
A = 1/7
b)
B = 6/5 / (1/15 - 1/5)
B = 6/5(1/15 - 1 x 3/5 x 3) B = 6/5 / (1/15 - 3/15)
B = 6/5 / - 2 / 15 B = 6/5 * - 15 / 2
B = - 90/10
B = 10 x 9/ 10 x 1
B = - 9
