the correct question is
Keiko sold 3 less than three-fourths of his sister’s sales. Which expression represents what Keiko sold?
Let
S----------------> the amount that Keiko's Sister sold
K----------------> the amount that Keiko sold
we know that
Keiko sold 3 less than three-fourths of his sister’s sales
K=(3/4)*S-3
the answer is
K=(3/4)*S-3