the slope should be - ⁵/₃ because its perpendicular
by trying the options
A =
3x - 5y = 20
-5y = 20-3x
y = -4 + ³/₅x
so A is incorrect
Option B
3x + 5y = 20
5y = 20-3x
y = 4 - ³/₅ x
So option B is incorrect
Option C
5x + 3y = 21
3y = 21 - 5x
y = 7- ⁵/₃ x
so Option C is the correct answer