25 points!
i don't need an answer, just an explanation of how to do it. )

1st Apply rule -(-a) = a

    1 + 3

2nd Add the numbers: 1+3=4

Hope I helped you out :)

See below.

Step-by-step explanation:

2 adjacent negatives like we have here simplify to a +.

1 - (-3)

= 1 + 3

= 4.

The product of 2 negative values is always a positive for example:

-2 * -3 = 6.

We can look upon -1(-3) as a product of -1 and - 3 , giving +3.

3x + 4y -25 =0 represents the amount of change sianna should recieve