An empty box weighs 200g the box is filled with birthday party goozy bags and now weighs 6.2kg each goody bag weighs 150work out how many goody bags are inside the box

For this case, the first thing we are going to do is define variables.
 We have then:
 x: number of birthday party goozy bags
 y: total weight
 We then have the following equation:
 y = 150x + 200
 For y = 6200 we have:
 6200 = 150x + 200
 Clearing x:
 x = (6200-200) / (150)
 x = 40
 
 there are 40 goody bags inside the box

The vertex of the quadratic function is (1.5, -.75)