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.