Angle 0 is in quadrant 1 with sin0 = 2/5. use the pythagorean identity, sin^2 0 + cos^2 0 = 1, to calculate the value of cos0 as a radical.

We know that
sin²x+cos²x=1
so 
clear cos x
cos x=(+/-)√[1-sin²x]

in this problem
Angle 0 is in quadrant 1 > cos o and sin o are positive
sin o=2/5
cos x=√[1-(2/5)²]> cos o=√[1-4/25]> cos o=√[21/25]---> cos o=√21/5

the answer is
cos o=√21/5

The answer is c because you turn 17.5% into a decimal which gives you .175 then you times that by $361.35 which gives you 63.23625 but then you round that which gives you 63.24. then you at 63.24 pulse 361.35 and you round it which gives you $425