I read a post below about using the "if" function for multiple calculations
inside of 1 formula, but I did not quite understand your responses.

My issue is taking 13 values from say cell "L3" and multiplying that value
by a specified formula:
=IF(L3=4,D3+50,IF(L3=6,D3*1.5+50,IF(L3=8,D3*2+50,I F(L3=10,D3*2.5+50,IF(L3=12,D3*3+50,IF(L3=14,D3*3.5 +50,IF(L3=16,D3*4+50,IF(L3=18,D3*4.5+50,))))))))
Problem being I have 5 more values to add 20,22,24,26,28 how do I do this?
It appeared to me that I needed to incorporate the "or" function but when I
did this it returned an error. Thanks in advance