0.8 = 8 tenths.
1 tenth = 0.1 = 1/10
8 tenths = 0.8 = 8/10.
8/10 divide both the numerator and denominator by a common factor that is the greatest. In this case is 2.
After doing so, the result should be 4/5.
We know that 5 lbs of apples cost $2.99
To know how much do 3 lbs of apple cost, you can use cross multiplication
If 5 lbs cost $2.99
Then 3 lbs cost $x
The proportion between the price and the number of apples is the same, you have to calculate it as:

3 lbs of apples cost $1.79
-2 because I’m just going to guess because I can’t see the system of equations
I think it’s the last one