A Manufacturer Has Been Selling 1,200 Television Sets a Week $p(x)=0.5 x+1,000$

A manufacturer has been selling 1,200 television sets a week at $400 each. A market survey indicates that for each $30 rebate offered to the buyer, the number of sets sold will increase by 60 per week. Find the demand function.

A) $p(x) =0.5 x+1,000$
B) $p(x) =-0.5 x+1,000$
C) $p(x) =-0.5 x+400.5$
D) $p(x) =-0.5 x+600$
E) $p(x) =0.5 x$