When 5 adult join a group of y diner the ratio of the number of adults to children in the restaurant became 3: 5. express the number of children in terms of y

When 5 adults joined the group of y: y+5

The ratio of the number of adults to children became 3:5, so the number of children to total diner should be 5:8. (8=3+5)

So the number of children would be (5/8)*(y+5) = (5y+25)/8