10 - 2x = -30
-2x = -40
2x = 40
x = 20
Y=2x+320
x being the number of years and 320 being the initial population of mice
We have to add 8/15 to 2/5.
To add two fractions we have to make them have the same denominator, so we have to convert 2/5 to have a denominator of 15. To do this, we have to multiply 2/5 by 3 and then we can add the fractions:

Answer: 14/15