Please help me with creating formula:

Cell A1 = 1 value (example 5000)
Cell A2 has only 3 values: 40, 60, 80
Forumla in Cell A3:

If A2 = 40 then A1 - 140

A1=5000
A2=40
A3=4860

If A2 = 60 then A1 - 180

A1=5000
A2=60
A3=4820

If A2 = 80 then A1 - 220

A1=5000
A2=60
A3=4780

Please help me creating forumula in cell A3, but important is cell A2
because
it has only 3 values 40,60,80