SEAMO 2027 - Paper C - SET 07 - Self-study Question 12

Given $\frac1{1\times5}+\frac1{5\times9}+\frac1{9\times13}+\frac1{13\times17}+\frac1{17\times21}+\frac1{21\times25}=\frac mn$, where $m,n>0$ are relatively prime integers, find $m+n$.