Two numbers total 77 and have a difference of 21. find the two numbers

So we can create two expressions to represent these.
X+Y=77
X-Y=21
we can use substitution or elimination
let's rearrange one of the equations.
let's make X-Y=21. let's move the y over!
X=y+21 now we can plug it in to the other equation!
y+21+y=77
2y+21=77
move 21 over..
2y=56
y=28! just use this value to find X
use any equation you want.
X+28=77
X=49
two values are 49 and 28

Yes, two vertical lines can be complementary