Question 124538
Use the distance formula on this problem:
{{{d = rt}}} where:d = distance, r = rate(speed) and t = time of travel.
For the first trip:
{{{t[1] = 6}}} and we don't know {{{r[1]}}} 
For the second trip:
{{{t[2] = 4}}} and {{{r[2] = r[1]+20}}}
and, of course, d is the same in both cases.
So, we can write:
1) {{{d = 6r[1]}}} and...
2) {{{d = 4(r[1]+20)}}} setting these two equal to each other and simplifying...
{{{6r[1] = 4r[1]+80}}} Subtract {{{4r[1]}}} from both sides.
{{{2r[1] = 80}}} Divide both sides by 2.
{{{r[1] = 40}}} Now we can find the distance, d.
{{{d = r[1]t[1]}}} Substitute {{{r[1] = 40}}}and{{{t[1] = 6}}}
{{{d = 40*6}}}
{{{d = 240}}}km.
Check: Substitute {{{r[2] = r[1]+20}}} and {{{t[2] = 4}}}
{{{d = r[2]t[2]}}}
{{{d = (40+20)*4}}}
{{{d = 60*4}}}
{{{d = 240}}}km.
The distance from town A to town B is 240 km.