a quantity with an initial value of 5100 decays exponentially at a rate such that the quantity cuts in half every 4 seconds. what is the value of the quantity after 0.45 minutes, to the nearest hundredth

Talia took the bus from her home to the bank and then walked back to her home along the same route. the bus traveled at an average speed of 40 km/h and she walked at an average speed of 5 km/h. to determine the time, x, that it took talia to walk home, she used the equation 40(0.9 – x) = 5x. the time of trip 2 is hours. the distance of trip 1 is km.