jbaldyga

Thai Baht f = -1.25%
Thai I = 3%
f = Thai I - Philline I or -1.25 = 3 - X
solve for X: X = 3 - (-1.25) = 3 + 1.25 or 4.25%
since the PHP is a discount, f is a negative #.
Does that answer your Q?