Can you show how to solve this?

A competitive rm uses three-factor production. Its production function is given by KW = (x + y)1'221'2. The factor prices used to be Bx: $1, RR = $2, and V131: $3. The prices of x and 2 decreased to half of their previous levels, but the price of factor y stayed constant. Then the cost of production a. decreased by more than 1/2. b. decreased by 1/3. 0. decreased by exactly 1/2 d. stayed constant. e. decreased by less than 1/3