Answer:
Then 1/2 or  30 minutes is the required time for Tom to cover the exact distance that Linda one hour before.
Two hours after Tom began Tom would cover 12 miles and three hours after Linda started Linda would be 6 miles far away from the starting point
Step-by-step explanation:
Linda walks in a straight line at 2 miles/hour
then after t ( hours time) she is   2 (m/h) * t  = d (L)
for Tom running at 6 m/h starting one hour later to cover the same distance d(L)
d(L) Â = Â 6 m/h * ( t - 1 ) Â Â then:
2 (m/h) * t  =  6 m/h * ( t - 1 )
2*t  =  6*t - 6
4*t = 6
t = 6/4
t = Â 1,5 h
Checking that result.
we see that in 1,5 hours Linda has covered  2* 1,5  = 3 miles
and  in 0.5 hours  Tom covered the same distance  0,5 * 6 = 3 miles
NOTE: Remember that tom started one hour later.
Then 1/2 or  30 minutes is the required time for Tom to cover the exact distance that Linda one hour before.
b) Â In this case
d(T) = 6* ( t - 1 )    must be equal  to  twice of the Linda distance
d(L) Â = 2 * 2 * t
6*t - 6 Â = Â 4*t
2*t  =  6
t  = 3
To check it
in 3 hours  Linda had covered  3 * 2  =  6 miles
in 2 hours  Tom had covered  2 * 6  =  12 miles