Need help!! Show work if possible and no rounded decimals!

Answer:
Q9. a) f(x)= -2x²+40x
b) maximum area= 200 ft²
dimensions= 10ft × 20ft
Q10. 210 bracelets, $3150
Step-by-step explanation:
Please see the attached pictures for the full solution.
For Q9(a), the function is found by multiplying the length and breadth of the garden to find the area.