Call the two resistors 'x' and 'y'.
In series, the resultant resistance is their sum: x + y = 108
Notice that y = 108 - x. I think we'll use that very soon.
In parallel, the resultant resistance is (their product) / (their sum) = xy/108 = 24
Multiply each side by 108:
xy = 2,592
Substitute for 'y' :
x(108 - x) = 2,592
108x - x² = 2,592
-x² + 108x - 2,592 = 0
x² - 108x + 2,592 = 0
Use the quadratic formula to find:
x = 72 . . . then y = 108 - 72 = 36
or
x = 36 . . . then y = 108 - 36 = 72
The individual resistors are 36Ω and 72Ω .