Can some one explain to me how this problem was sloved ? Plz

on friday there were 15 birds

for this case we have by definition, if two lines are perpendicular, then the product of their slopes is -1.

then, given the following line:

so,

we are looking for m_ {2}:

then, the line is given by:

we find "b" replacing the given point:

finally, the equation is:

option c

the cost of the pair of pants is $31.95