Remark
Interesting way to teach this problem. I'll see if I can make a table that answers the question as it is presented.
Now all you need do is collect the nine terms from the table and put the like ones together if there are any.
Answer:
4.5
Step-by-step explanation:
I think it will work if you Divide 54 over 12 = 4.5
The slope of the line through (1,0) and (3,8) is 4
A good estimate for a door in a public setting is about 4 feet

We rewrite it in a more functional form:

I'll make a vertical table, easier to type. For each x we subtract 3 to get y.
x y
0 -3
1 -2
2 -1
3 0