You basically have 4 conditions. Check for the hard set ones first then do the multiplier last.
so we will check for 10 11 or 21
=if(A1=10,1.00,"")
=if(A1=11,1.05,"")
=if(A1=21,2.05,"")
Now put them all together
=if(A1=10,1.00,if(A1=11,1.05,if(A1=21,2.05,"")))
No we need to add a...