The answer is 10 pairs of shoes.
The first ratio is 10:5. 10 socks per 5 pairs of shoes. You have 20 socks now instead of 10. You just double the ratio. 20 socks per 10 pairs of shoes. 20:10.
√m/3 = 4
To remove the radical sign, square both sides.
(√m/3)² = 4²
m/3 = 16
To remove the denominator of 3, multiply both sides by 3.
3 (m/3) = 3(16)
m = 48
To check: Substitute m by its value.
√m/3 = 4
√48/3 = 4
√16 = 4
4 = 4
The answer I think should be
C main