Remark
This may be a little confusing, but because they are travelling in opposite directions, the distances add when you want to get how far apart they are.
d1 + d2 = 1541
Equation
Let the time this happens = t
d1 = 323*t
d2 = 347*t
323*t + 347*t = 1541 Combine like terms on the left.
670t = 1541 Divide by 670
t = 1541/670
t = 2.3 hours pass before the distance of 1541 miles are between the two planes. You might need the answer to be 2 hours 18 minutes.