The equation is .
(Write the equation)
Apply addition property of equality: if .
(Add 13 to each side)
(Apply commutative property of addition:
(Apply additive inverse property:
)
(Apply additive identity property:
)
(Add:
)
Check whether is a solution.
(Write the equation)
(Substitute
)
(Subtract:
)
is a solution.
The solution is .