Question

a party of people go for an excursion in x cars, of which y cars each hold 4 people and the remainder 5. How many people were their in the party

Answer 1

4y+5x

So much for math -- now it's time to ask for help with English.

Answer 2

Oops. My bad.

4y + 5(x-y) = 5x-y

You can think of the party as having x cars of 5 people each, then subtract one person for each of the y cars, which only hold 4.