Tom drove away from Bigtown 10 minutes after Janice, and overtook her in 20 minutes, ?

if Tom drove at a speed of 90mph, what was Janice's speed in mph? Tom drove away from Bigtown 10 minutes after Janice, and overtook her her in 20 minutes, If Tom drove at a speed of 90mph, what was Janice's speed in mph?_____