We can start by rewriting the equation:
x + 6y = 18
Because we already have our y-coordinate, we can plug it in for the equation.
x + 6(5) = 18
Now we can simplify.
x + 30 = 18
Since we are adding 30 to a number to get another number less than 30, we can presume that x equals a negative number. 30 - 18 = 12. That means that x would equal -12.
Now we can plug -12 in as x to see if our equation is valid.
-12 + 30 = 18
Because negative 12 added to 30 does equal 18, we know that our equation is correct.
Your final answer: The missing coordinate is -12. The final ordered pair is (-12,5). If you need help understanding, let me know and I will gladly assist you.