Question 1125758
x to y
traveled {{{70*2=140}}} miles
before the other train began.


y to x
traveled, {{{20*t}}} miles.


Just before y to x train began,  first train went 140 miles, so distance between trains was  {{{320-140=180}}} miles.



When both trains were moving toward each other,

{{{(70+20)t=180}}}
{{{t=180/90}}}
{{{highlight(t=2)}}}


The two trains meet after {{{2+2=highlight(4)}}} hours.