9. For the equation x2y2 + 3x3y &mdash; xy4 &mdash; 14 = 0，tlie slope of the tangent line at the point (-1,2) is=____

2. A motorcycle shop estimates that it will soil 750 motorbikes in a year. Eacli biko cost $300, plus a fixed charge of $400 per order. If it costs $240 to store a motorbike for a year, what is the order size and how many orders will be needed in a year to minimize inventory costs?