Suppose the cost function for a company $is$ given $by$ the following equation, where $xis$ the number $of$ units $of$ phone chargers and $yis$ the number $of$ units $of$ phone covers produced. Complete parts $(a)$ and $(b)$ below.

$C(x,y)=630x+90y+3700$

$(a)InC(x,y),$ what does $3700$ represent?

$A.3700$ represents the marginal cost $of$ producing one more phone cover when the number $of$ phone chargers $is$ held constant.

$B.3700$ represents the fixed costs, $or$ the cost when $no$ items have been produced.

$C.3700$ represents the fixed cost, $or$ the cost when $3700$ phone chargers and phone covers have been produced.

$D.3700$ represents the marginal cost $of$ producing one more phone charger when the number $of$ phone covers $is$ held constant.

$(b)$ Find $\frac{\text{d}\text{e}\text{l}\text{C}}{\text{d}\text{e}\text{l}\text{x}}$ and $\frac{\text{d}\text{e}\text{l}\text{C}}{\text{d}\text{e}\text{l}\text{y}}.$ What $do$ these quantities represent?

$\frac{\text{d}\text{e}\text{l}\text{C}}{\text{d}\text{e}\text{l}\text{x}}=$