
Substituting this into the other ODE gives

Since
, it follows that
. The ODE in
has characteristic equation

with roots
, admitting the characteristic solution

From the initial conditions we get



So we have

Take the derivative and multiply it by -1/4 to get the solution for
:

Each bike has two tires, while each quad has four tires. Therefore the number of tires Ruby has to other is given by the number of tires used by the bikes added by the number of tires used by the quads. This is shown on the expression below:
Answer:
The y value of a point where a vertical line intersects a graph represents an output for that input x value. If we can draw any vertical line that intersects a graph more than once, then the graph does not define a function because that x value has more than one output.
17 and a half cups would be the answer because of the poopo