What three even numbers add up to 54

X = lowest
x+2 = middle
x+4 = largest

x +      x+2 +    x + 4 = 54

Combine like terms to get 3x + 6 = 54
Subtract 6 (both sides)           -6     -6
                                       3x = 48
divide by 3 (both sides)     3       3

x = 16 (smallest even number)   x+2 = 18 (middle even number and x+4 = 20 (largest even number)   Add them up 16+18+ 20 and sure enough, you get 54

The way I like to do these is like this ... without algebra:

-- If the 54 were split up into three equal pieces,
each piece would be 1/3 of 54 = 18 .

-- Can you take three equal size-18 pieces and change them in
such a way that they're all different but their sum doesn't change,
and they still add up to 54 ?

-- How about like this: 
Take 2 away from one piece and glue it onto a different one.
Now they still make the same 54 when you put them all into the same pot. 
But now they're all different ... instead of 18, 18, 18, now you have 16, 18, 20.

Look ma !  No algebra !