Question 740750
At any given time they form a  right angle with the starting point.

100 miles apart
hypotenuse = 100

car x miles
train (x+20) miles

apply Pythagorean theorem

x^2+(x+20)^@=100^2

x^2+x^2+40x+400=10000

2x^2+40x-9600=0

/2
x^2+20x-4800

x^2+80x-60x-4800=0

(x+80)(x-60)=0

ignore negative
x= 60

car 60 miles
train 80 miles