Numerator 6x - 18 = 6(x - 3)
Denominator x^2 - 5x + 6 = (x - 3)( x - 2)
Observe the given data distribution table carefully.
The 5th class interval is given as,

The upper limit (UL) and lower limit (LL) of this interval are,

Thus, the upper-class limit of this 5th class is 17.4.