A boy walks for x hours at 33 mph and bicycles for (5−x) hours at 93 mph. If the total distance traveled is d miles, express d in terms of x.

speed = distance/time, so

distance = speed * time

Walking:
d = speed * time
d1 = 33 mph * x hours = 33x miles

Bicycling:
d = speed * time
d2 = 93 mph * (5 - x) hours = 93(5 - x) miles = (465 - 93x ) miles

The total distance traveled is the distance walked plus the distance bicycled

d = d1 + d2

d = 33x + 465 - 93x

d = -60x + 465