I will do 12 only.
Let x = cost per pants.
A function for pants is f(x) = 5x.
Let y = cost per shirts.
A function for shirts is f(y) = 3y.
Let z = cost per pair of shoes.
A function for pair of shoes is f(z) = 11z.
For selling 12 pants:
f(12) = 5(12) = $60.
For selling 21 shirts:
f(21) = 3(21) = $63
For selling 6 pairs of shoes:
f(6) = 11(6) = $66
Let S = what she earned in total sales.
S = $60 + $63 + $66
S = $189
