formula in an IF function doesn't work, syntax?

Here is the formula I am trying to make work: =IF(L6>55000,"(((L6-55000)/1000)*2.1809)+(55*1.69)","((L6/1000)*1.69)") which I built using the formula builder but the result just keeps returning the formula in the cell where I entered it. I can make the formula parts work individually, but they fail when I put it all together in the IF.

I have a situation where we pay 2 different rates per thousand depending on how much a we use. The 1st 55 thousand costs 1.69 per thousand, all that used above 55 thousand costs 2.1809 per thousand. Since the amounts vary both less than 55 thousand and above 55 thousand, I need to test and then apply the correct formula(s) to get the result.

L6 has a value of 65,000. If it is greater than 55,000 I want to calculate the amount used greater than 55,000 and apply the correct rate per thousand for that usage and then apply the correct rate for the 1st 55 thousand used and add the 2 results together > the TRUE IF, otherwise I just want to apply the less than 55 thousand rate to amount used, the FALSE IF.



so
65,0000 - 55,000 = 10,000/1000 x 2.18 for the amount over 55,000 plus 55*1.69 for the 55,000. Since in the example L6 is 65,000 the formula parts for TRUE should be 10*2.18 + 55*1.69 = 20.18 + 92.95 and the cell with formula should display 113.13; I rounded this example a little.

I know I am missing something easy here, just don't know what. Thank you for looking showing me where I screwed up.