Question 12055
Let n be the number you are looking for.

From the description, you can write:

{{{(2/5)n - (3/4) = 7/8}}}  Let's clear the fractions by multiplying through by the common denominator of 40.

{{{40(2/5)n - 40(3/4) = 40(7/8)}}}
{{{16n - 30 = 35}}} Add 30 to both sides.
{{{16n = 65}}} Divide both sides by 16.
{{{n = 65/16}}} = 4 1/16

The number is: 4 1/16 That's 4 and 1/16

Check: 

{{{(2/5)(65/16) - (3/4) = 13/8 - 6/8}}} = 7/8