To find a value (or values) we can put in place of a variable that makes the equation true.
Example: x + 2 = 7
The variable is x,
when we put 5 in place of x we get 5 + 2 = 7,
and 5 + 2 = 7 is true, so x = 5 and the equation is solved.
(Note: if we said x=6 then the equation is not solved because 6+2=7 is not true)
