Question 1186798
 the initial time {{{t}}}
 the initial speed {{{s }}}

if speed is increased by {{{20}}} percent : 
{{{s+0.20s}}}

time reduced {{{15}}} min
{{{t-15}}}


{{{st=(s+0.20s)(t-15)}}}
{{{st=1.2 s (t - 15)}}}
{{{t=1.2t - 18}}}
{{{18=1.2t - t}}}
{{{18=0.2t }}}
{{{t=18/0.2}}}
{{{t=90min}}} ->the initial time taken by the person