An investment broker wants to invest up to $20,000. she can invest in two mutual funds based on their yearly average return for the 5 years ending december 31, 2009: the franklin natural resources fund yielding 10% and the oppenheimer developing markets a fund yielding 15%. she wants to invest at least $5000 in the franklin natural resources fund and no more than $8000 in the oppenheimer developing markets a fund. how much should she invest in each type of fund to maximize her return?