(3,4) (-3,8) ( 6,8) is a function?

The relation {(3, 4), (-3, 8), (6, 8)}, is a function, because

all the x–coordinates are different.

It's important to understand that even though two of the y-coordinates

are the same, this relation is still a function.

The y-coordinates do not have any affect

on whether the relation is a function.

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.

you can use a^2+ b^2=c^2