Question

Assume that x and y are differentiable functions of t. Find dy/dt using the given values.
xy=x+4 for x=4, dx/dt=-5

a. 0.20

b. 3.75

c. 1.25

d. 5.00

e. -0.25

Answer 1

from xy = x + 4
x dy/dt + y dx/dt = dx/dt + 0

when x = 4 , in original
4y = 4+4
y = 2

so when x=4, y=2 and dx/dt = -5

4dy/dt + 2(-5) = -5 + 0
4dy/dt = 5
dy/dt = 5/4 which is c)

Answer 2

is it C. or D.