The angle is 60° because
B is a right angle and that adds to 90°, so dividing 90 by 3 would get 30
30 x 2 = 60
and to check the answer
x = 30
A=30
B=90
C=60
this adds to 180 which is correct because the angles in a triangle add to 180° :)
When x=-1:

Ok that gives us a little more information.
If we implicitly differentiate with respect to t, from the very start, then we can apply our product rule, ya?

The right side is zero, derivative of a constant is zero.
Where x' is dx/dt and y' is dy/dt.
From here, plug in all the stuff you know:
y' = -3
x = -1
y = 4
and solve for x'.
Hope that helps!
Answer:
Step-by-step explanation:
378 feet
Its to long to explain but thats the answer
-3x+5y=30
+3x+5y=30
5y=3x+30
divide 5 by everything
answer: y=3/5x+6