A multiple regression model between sales $($y in $$1,000),$ unit price $($x$1$ in dollars$),$ and television advertisement $($x$2$ in dollars$)$ resulted in the following function:

y $=11+3$x$1+4$x$2$

For this model, SSR $=2500,$ SSE $=550,$ and the sample size is $20.$ The coefficient of the unit price indicates that if the unit price is:

a$.$ increase by $$1($holding advertisement constant$),$ sales are expected to decrease by $$3.$

b$.$ decreases by $$1($holding advertisement constant$),$ sales are expected to decrease by $$3,000.$

c$.$ increase by $$1($holding advertisement constant$),$ sales are expected to decrease by $$300.$

d$.$ increase by $$1($holding sales constant$),$ sales are expected to increase by $$3,000.$

e$.$ none of the above.