Answer:
893 snakes after first year
Explanation:
total population= 900
death = 30 per year left= 900-30= 870
birth each year= 20 per year so 870 +20= 890 snakes
6 snakes migrate into the population = 890 + 6= 896 snakes
3 migrate out of the population per year = 896-3= 893 snakes