Question 840944
Distance = Rate * Time
{{{D[1]=15*T}}}
{{{D[2]=20*T}}}
Since one is going north and the other is going east, their distances are legs of a right triangle and the distance between them is the hypotenuse of the right triangle. Use the Pythagorean theorem.
{{{D^2=D[1]^2+D[2]^2}}}
{{{D^2=(15T)^2+(20T)^2=75^2}}}
{{{225T^2+400T^2=5625}}}
Take it from there to solve for {{{T}}}