The first car would have already travelled 60 miles north when the second car sets off.
After time t hours the first car would travel an additional 30t miles north while the second car would travel 25t miles east. The total distance for the first car is 60+30t, and the hypotenuse of a right triangle is their distance apart=√((60+30t)2+(25t)2)=300, 3600+3600t+900t2+625t2=90000.
1525t2+3600t=86400, 61t2+144t-3456=0. Using the quadratic formula, t=6.4387 hrs, (6hr 26.32min approx). This is the positive root. But t is time measured by the second car, so we have to add two hours to this: 8.4387hr or 8hr 26.32min.