IF: x – y = z
THEN: 3(x – y) = 3z

This is a true statement.

Step-by-step explanation:

Whatever you do to one side of an equation, you must do the same to the other side. If you know that x - y = z, then if you multiply both sides by 3, they are still equal.

for finding the midpoint of any given 2 pair of points simply add the respective x coordinates with other x coordinate and the y coordinate with other y coordinate and divide them by 2

in your question it will be :

(3+1)/2 for the x coordinate of mid point i.e 2

[8+(-4)]/2 for the y coordinate of midpoint i.e 2

so coordinates of mid point of points (3,8) and (1,-4) will be (2,2)

add all the numbers and check the ones place.

the answer is 486. as the ones place is more than 4, the estimation will be the next 10 ie, 490