Area of the trapezoid 1/2 3ft 5 ft 2 ft

What your teacher wants is for you to isolate y in the given equation. In other words, get y all by itself. 

To do this, you'll do two basic steps:
Step 1) Subtract 2x from both sides
Step 2) Divide both sides by 3

Let's do that and we get...
2x+3y = 1470
2x+3y-2x = 1470-2x ... apply step 1
3y = 1470-2x
3y = -2x+1470
3y/3 = (-2x+1470)/3 ... apply step 2 
y = (-2x)/3 + 1470/3
y = (-2/3)x + 490

After isolating y, we get y = (-2/3)x + 490
To get this into function notation, we simply replace y with f(x) to get the final answer f(x) = (-2/3)x+490 which is the same as writing 

This graph represents all of the ordered pairs (x,y) that make the original equation true. For example, the point (x,y) = (0,490) is on the line where x = 0 and y = 490. This point is when 0 sandwiches are sold and 490 wraps are sold yielding a profit of $1470. Another point on this line is (x,y) = (3,488). Now 3 sandwiches have been sold along with 488 wraps leading to the same profit of $1470. Any ordered pair point you pick on the line should lead you to the same profit.