Question

−4x + 3y = 15, where x is time and y is velocity in kilometers per hour. Use this function to determine when a certain particle will reach 40km/hr.

Answer 1

You need to substitute y for the 40 km/hr.
So -4x + 3(40) = 15
-4x + 120 = 15
-4x = 105
x = 26.25 sec

Answer 2

26.25 hours = 26 hours 15 minutes

substitute y = 40 into the equation and solve for x

- 4x + 120 = 15 ( subtract 120 from both sides )

- 4x = - 105 ( divide both sides by - 4 )

x = 26.25 hours = 26 hours 15 minutes