f.1 maths question~plz help..............((fast......))

Question

city A is 100km to the west of city B. David rides a bicycle 15km/h from city A to the west. At the same time, Alice drives a car Y km/h from city B to the west.

a)Express in terms of Y, the distance between David and Alice after 2 hours.

b)If Alice catches up with David after 2.5 hours , find the value of Y.

請列明步驟！thx@@@

Answer 1

a)
the distance between David and Alice after 2 hours
= 100 - 2Y + 2 x 15
= 100 - 2Y + 30
= 130 - 2Y

b)
100 + 15 x 2.5 = 2.5Y
137.5 = 2.5Y
Y = 55

Answer 2

a)100 - 2Y + 2 x 15
= 100 - 2Y + 30
= 130 - 2Y

b)100 + 15 x 2.5 = 2.5Y
137.5 = 2.5Y
Y = 55

Answer 3

a) Distance between David & Alice is
= (15 X 2 + 100 ) - Y X 2

b) 0 = (15 X 2.5 + 100) - Y X 2.5
2.5Y = 137.5
Y= 55 km/h