Algebra Word Problem-HELP!

I have been working on this math problem for days and can't seem to figure it out. My math book does not have any examples like this at all. I cannot figure out how to find a quadratic function for this information (I can only seem to find a linear equation). I typed the exact question below and if anyone can help or give any advice at all that would be great! Thanks.

You are given the task of estimating the number of trees that will maximize the fruit production per acre of a local orchard. By researching other local orchards you discover that at 400 trees per acre each tree will produce an average of 30 pounds of fruit. For each tree that is added to the acre, the average production **per tree** goes down 0.05 pounds.

a. Use the given info to build a table of values for this situation. Let *t *be the number of trees above 400 planted on an acre and find the total amount of fruit each acre will produce.

b. Find a function for the total production per acre when *t *trees over 400 are planted on one acre.