Question 214012
Imagine you have a stopwatch. You start it at 
the exact moment that Ed is 15 mi behind Connor.
You will stop the stopwatch at the exact moment
Ed catches Connor. That means they are both
going to be driving for the same length of time.
You also know that Ed will have to drive 15 mi more
than Connor to catch him.
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You need 2 sets of equations, one for each driver
{{{d[c] = r[c]*t[c]}}}
and
{{{d[e] = r[e]*t[e]}}}
You already know that {{{t[c] = t[e]}}} (call them both {{{t}}})
And {{{d[e] = d[c] + 15}}}
given:
{{{r[c] = 65}}}
{{{r[e] = 70}}}
Now rewrite the equations
{{{d[c] = 65t}}}
{{{d[c] + 15 = 70t}}}
And by substitution,
{{{65t + 15 = 70t}}}
{{{5t = 15}}}
{{{t = 3}}} hrs
Ed will catch Connor in 3 hrs
check answer:
{{{d[c] = 65t}}}
{{{d[c] = 65*3}}}
{{{d[c] = 195}}} mi
and
{{{d[c] + 15 = 70t}}}
{{{195 + 15 = 70*3}}}
{{{210 = 210}}}
OK