I want a function that will put a cost amount in the Cost column based on
Plan type; for example if Plan=C then cost will be 6.17 if Plan=A then cost
will be 7.10.

I am not sure if this should be an IF(OR) statement or some other function
and how to write that function.

example

Item Plan Cost
xxx C 6.17
xxx A
xxx C
xxx A
xxx C

Thanks in advance