Let t = the number of toppings ordered.
The cost of a pizza will be 17 + 1.2 t and that must be less than or equal to 20. I have removed the dollar indications for the purpose of simplicity.
Since we only have 20 to spend,
17 + 1.2 t ≤ 20
We could stop here, because that's all the problem asked for, an inequality, and not its final solution.
Note that taxes, a possible tip, and other incidentals have not been accounted for.
To solve this, we could subtract 17 from both sides, resulting in:
1.2 t ≤ 3 and dividing by the coefficient of t, 1.2, we arrive at:
t ≤ 3/1.2
Since t must be a whole number (fractional topping amounts make no sense), we know that
t ≤ 2
So t must be either 0, 1, or 2 toppings.
