Travel problems I just dont understand Richard drove his rig

Travel problems I just don\'t understand. Richard drove his rig at \'x\' mph for 3 hours, then increased his speed to (x+15)mph and drove 2 more hours. Wrtie a polynomial that represents the total distance that he traveled. how much distance did he covered if x=45 mph?

Solution

Ok first you need to know the equ.s for speed, distance and time.
Speed= distance x time
Distance= speed/time
Time= speed/distance
You need to figure out what distance this guy drove for at each speed and then add the together to find the total distance.
Step one :
Write down eq\'s for the two speeds but solving for distance
D1=x/3 then D2= (x+15)/2
D1+D2=Total distance
We know x=45 so we sub 45 in for the all the x\'s and solve
D1=x/3 D2= (x+15)/2
=45/3 = (45+15)/2
=15miles =30 miles
D1+D2= total
15 miles+ 30 miles= 45 miles
Therefore he travled 45 miles
** be sure to include all steps and units for full marks