Suppose labour and capital are perfect complements. In particular, the producer needs to use 2 units of labour for each unit of capital. Suppose the producer is currently facing input prices w=$1 and r=$1, and is currently using bundle (L,k)=(4,2) which allows him to produce 4 units of output. What is the increase in the cost of producing those 4 units of output if w were to increase to $2 (while r remains at $1)?