So we have 2 variables here: tacos and orders of nachos.
When we translate the paragraphs into equation:

Now, in this situation we can make use the elimination method by converting 3n to -27n.

Add both equations:

So we find that one taco costs $2.75.
We can plug this into any of the first two equations to find n:

So one order of nachos cost $1.40.