What is the slope of the line with equation y=12x

  When you have an equation of the form y = mx + b (which you do in this case), the slope is always equal to the coefficient of x, which is m or 12 in this case. Since there is no "b" in your equation, you could say that b=0, and the line is known to cross the y axis at zero. 

In case you are interested, if the equation said y = 12 x + 3 the slope of the line would still be 12 but the line would cross the y axis at 3. If the equation said y = 12x -4, the line would have a slope of 12 and would cross the y axis at -4.

If you need an equation, it would be y=2x+8, y would be how long it grew, x being weeks.if you need how long he was asleep, it would be 4 weeks if he started with no beard, the equation would be x=8÷2if he did have a beard before hand, the equation would be 2w+x=8