Let $z = x + y$ , and Let $x$ And $y$ Be Functions Of

Multiple Choice

Let $z = x + y$ , and let $x$ and $y$ be functions of $S$ and $t$ with $x ( 0,0 ) = 1 , y ( 0,0 ) = 2$ , $\delta x / \delta s = 3$ , and $\delta y / \delta s = 4$ at $( s , t ) = ( 0,0 )$ . Find $\delta z / \delta \text {s }$ when $( s , t ) = ( 0,0 )$ .

A) 5
B) 6
C) 7
D) 8
E) 9
F) 10
G) 11
H) 12