Sorry about the parenthesis disfigure. I have worked it out. Also I have
simplified it for each format as written after OR.

The original format
(45c6 / (6c5 x (39c1 - 37c1)))

OR
45c6
( _________________________ )
(6c5 X (39c1 - 37c1))


The above format should become like this
((COMBIN(45,6))/((COMBIN(6,5))*((COMBIN(39,1))-(COMBIN(37,1)))))

OR

(COMBIN(45,6))
( _______________________________________________ )
((COMBIN(6,5)) X ((COMBIN(39,1)) - (COMBIN(37,1))))


Easiest way to convert is just enclose it in bracket. For example

xcy should become (COMBIN(x,y))

x and y is enclosed in a bracket with COMBIN outside enclosed again with
outer bracket.

The rest of the bracket in the original format will stay intact.