Where are you hung up?

Write down some definitions. <== Note: This is ALWAYS a great place to start.

B is the proportion in the Bond Fund

S is the proportion in the Stock Fund

B+S = 1, of course.

B >= 0

S >= 0

Write down the requirements and have at it.

"at least 30% of that amount will be invested in the bond fund"

B/(B+S) >= 0.30 or B >= (B+S)*0.30

"a mix will be selected that will enable a total return of at least 7.5%"

B*0.06 + S*0.10 >= (B+S)*0.075

After a little algebra, you'll be ready to start drawing pictures. Let's see what you get.