(a) Express \(\frac { 1 } { ( r + 6 ) ( r + 8 ) }\) in partial fractions.
(b) Hence show that
$$\sum _ { r = 1 } ^ { n } \frac { 2 } { ( r + 6 ) ( r + 8 ) } = \frac { n ( a n + b ) } { 56 ( n + 7 ) ( n + 8 ) }$$
where \(a\) and \(b\) are integers to be found.