Hi,
Since each bottle of glue has 2/5 of the entire thing, you would have to multiply 7 x 2/5
7 x 2/5 = 2.8.
The art teacher can have 2 full bottles of glue. Since 0.8 is left over, we can't just leave that out. So we need to have another bottle.
The final answer is 3 bottles of glue. Hope this helped and have a nice day!