To use repeated subtraction, you could keep subtracting 3 until you reach 0.
So, we can do
93-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3=0
This has 31 -3s,
So 91/3 is 31.
So do the opposite of the answer like for example 4 +3\2 and your answer is y
the you do the rest
1, Might not be precise
2, Can be hard to plot the graphs
3, If there are many solutions that will be really hard to plot sometimes.
This is just from the top of my head.
A number that is no more than 20 is less than