Illegal values for a multiplication statement are the values that make the denominator equal to zero.
To get the illegal values, factorize each denominator and get the values that make the denominator equal to zero.
For the first denominator:
c^2 + 5c - 14 = (c+7)(c-2)
For this term to be equal to zero, the c has to be either -7 or 2
For the second denominator:
c^2 - 2c - 15 = (c-5)(c+3)
For this term to be equal to zero, the c has to be either 5 or -3
Based on the above calculations, the illegal values of c in the given statement are:
-7 , 2 , 5 and -3