Question 754303
Proceed as follows:
1. What are they asking you?
You need a NUMBER that once you add {{{-7/20}}} to it,  you get {{{-2/5}}}

Now, let X be the number you dont know.

The question can be written as:

{{{X + (-7/20) = -2/5}}} (a number plus {{{(-7/20)}}} gives me {{{(-2/5)}}}

SOLUTION:

{{{X + (-7/20) = -2/5}}}
This is the same as:
{{{X -(7/20) = -2/5}}}
If you solve for X, you'll get:
{{{X = (-2/5) + (7/20)}}} (Notice how you have a negative (7/20) on the left side, and it turns positive on the right side)

{{{X = (-2/5) + (7/20)}}}
{{{X = (-1/20)}}}
This tells you that if you add {{{(-1/20)}}} to {{{(-7/20)}}} you'll get {{{(-2/5)}}}