Your answer is $120. You get this by first adding all of the fractions you were given by finding their common denominator. In this case, it is 24, which gives you
6/24 + 8/24 + 9/24 = 23/24. This means that the remaining $5 must equal 1/24 of his original allowance, so then we just need to multiply 5 by 24 to get the whole allowance, which equals $120.
I hope this helps!