I have no solution to proffer.  Since the alphameric scheme is not evident, then perhaps one of the letters could be assigned the value of the decimal point (i.e. ".") and then the right hand side might have "0.25000" (or various numbers of leading or trailing zeroes to keep the value 1/4. It would then seem we have to allow several different letters to map to zero, but you have already noted that there are 11 different letters.  The big problem with this line is assigning a value to "R" -- it would almost have to be zero to accomodate the two Rs on the right.  We might note specifically the LACK of the quondam caution that no number may begin with zero (perhaps that extends the range of possibilities a bit).  I agree the problems should intend a unique solution or state to the contrary.  Maybe someone will spot a witty trick in the wording which is contained in this brevity.