Write a simple if else logic in PHP

Hi I need to check a simple calculation using PHP. For example: I need 11 seats Now there are 3 vehicle showing which I am selecting using ****Checkbox**** =============================================================== Vehicle 1 = 10 seats Vehicle 2 = 8 Seats Vehicle 3 = 12 seats if I choose Vehicle 1 then an error will be shown that more vehicle needs after than If I choose Vehicle 2 then no error will show BUT after that, If I choose Vehicle 3 then an error will be shown. Another scenario ============== If I first choose Vehicle 3 then no error but after that, If I choose another Vehicle then an error will be shown. If you can do this then bid. All the code is ready. You just need to write this if and else statement in PHP. Write `10Nnow` in your bid. Thanks.