(a) \(\frac{2}{3}(3x - 5) - \frac{3}{5}(2x - 3) = 3\) \(\frac{10(3x - 5) - 9(2x - 3)}{15} = 3\) \(30x - 50 - 18x + 27 = 3 \times 15 = 45\) \(12x = 45 + 23 = 68\) \(x = \frac{68}{12} = 5\frac{2}{3}\) (b) \(n + r = 80^\circ .... (1)\) \(180^\circ - m + r = 88^\circ .... (2)\) From (1), r = 80^\circ - n. Putting into (2), we have \(180 - m + 80 - n = 88 \implies - m - n = 88 - 260 = - 172^\circ\) \(-(m + n) = - 172 \implies m + n = 172^\circ\).