Question 519582
s = speed
d = r*t is the distance equation
.
d = s*3 is the distance she travels in 3 hr now
.
d = (s+3.5)*2 is the distance she could travel in 2 hr if she went 3.5 km/hr faster
.
d = d
so
3s = (s+3.5)*2
3s = 2s +7
s = 7
.
s+3.5 = 10.5
.
Check the distances.
7*3 = 21
10.5*2 = 21
Correct.
.
Answer:  Her best average speed at present is 7 km/h.