## Elementary Technical Mathematics

$$-\frac{3}{8}rs^2+2rst.$$
By multiplying each term of the polynomial by the factor $-\frac{1}{8}rs$, and then adding the products, we have $$-\frac{1}{8}rs(3s-16t)=-\frac{1}{8}rs(3s)-\frac{1}{8}rs(-16t)\\ =-\frac{3}{8}rs^2+2rst.$$