How do i find the area of this triangle?

Answer question above and explain each step : )

Agreeting card company can produce a box of cards for $7.50. if the initial investment by the company was $50,000, how many boxes of cards must be produced before the average cost per box falls to $10.50?

In which direction does the left side of the graph of this function point? a(x) = 3x - x2 + 4x - 2