They donate:
[tex]500\cdot\frac{10}{100}=50\text{ sprouts}[/tex]then, 500 - 50 = 450 sprouts are left.
They sell:
[tex]450\cdot\frac{20}{100}=90\text{ sprouts}[/tex]then, 450 - 90 = 360 sprouts are left.
They plant in the greenhouse:
[tex]360\cdot\frac{5}{100}=18\text{ sprouts}[/tex]then, 360 - 18 = 342 sprouts are left.
The members plant 342 sprouts outside