Let the man's age be x.
400 - 3x = 163
First, simplify both sides of the equation.
400 + -3x = 163
-3x + 400 = 163
Npw, subtract 400 from both sides.
-3x + 400 - 400 = 163 - 400
-3x = -237
Finally, divide both sides by -3.
-3x / -3 = -237 / -3
x = 79
The man's age is 79 years old.