Starting at home, luis traveled uphill to the hardware store for 30 minutes st just 8mph. he then traveled back home along the same path downhill at a speed of 24 mph. what is his average speed for the entire trip from home to the hardware store and back?

1.
The main formula we use is :

Distance traveled = average Speed * Time,

in short:    D = S * T

2.
"luis traveled uphill to the hardware store for 30 minutes at speed 8mph."

we have the speed and the time = 30 min = 1/2 h

so we can find distance:

D=ST=8 (mi/h) * 1/2 (h)  =  4 mi

3.
Now we have D, and the speed 24 mph, so we can find the time it takes Luis to travel back home:

D=S*T

T= D/S = 4 (mi) / 24 (mi/h) =1/6 h

4.

The total distance is D+D = 4 +4 = 8 (mi)

the total time is 1/2 +1/6 = 3/6 + 1/6 = 4/6 = 2/3 (h)

So we can find the average speed of the entire trip is:

S=8 / (2/3)= 8* (3/2)=4*3=12 (mph)

Answer : 12 mph 

Hope i can you!