Can anyone help me get the php algorithm for the following condition?

Can anyone help me get the php algorithm for the following condition:

If x is less than 8 then display y=22, 
   else if x is equal to 9 but less than 25 then display y=25, 
   else if x is greater than 25 but less than 31 display y=30,

And if it's above 31 and to every succeeding of 5, add 3 from the previous display y+3:
   so if x is in the range of 31 to 35, display y=30(previous)+3,
   and so on if x is in the range of 36-40, display y=33(previous)+3,
   and so on if x is in the range of 41-45, display y=36(previous)+3