Answer:
y = -3x + 9
Explanation:
y = mx + b where m is the slope and b is the y intercept
The hypotenuse is on the same line as BC but twice as long. So extend that line up and it will cross the y axis at (0,9). 9 will be your y intercept.
To find the slope start at C and count up 9 and to the left 3 to get to B.
So the slope is rise/run or 9/(-3) = -3.
Final equation would be y = -3x + 9