Step-by-step explanation:
the slope is the factor of x in an equation
y = ax + b
we have here
3y = -5x + 21
to get to the general format above we need to divide everything by 3 :
y = -5/3 x + 7
so, we see, the slope is -5/3.
the perpendicular (angle of 90°) slope is the original slope turned upside-down and with flipped sign :
3/5
so, I guess the correct answer option is c.
but it is not clear what you wrote there, as there is a "-" sign somehow in all 4 answers.
