First, let's put 2/5 and 1/8 into similar fractions, in that they have the same denominator.
2/5 = 16/40
1/8 = 5/40
Then, we'll add the fractions together.
16/40 + 5/40 = 21/40
So, Jeff spent 21/40 of his money. We can set up a proportion to find the amount that Jeff spent.
x/20 = 21/40
420 = 40x
x = 10.50
Finally, we'll subtract the amount that Jeff spent from the original amount.
20 - 10.50 = 9.50
Jeff has D. $9.50 left.
Hope this helps!! :)