I'm doing some Calculus homework, but these two problems are a bit confusing. Thanks for taking the time to look:

Consider the curve defined by 2y^3 + 6x^(2)y - 12x^2 + 6y = 1

1. Find dy/dx (Found using implicit differentiation; (4x-2xy)/(x^2+y^2+1))

2. Write an equation of each horizontal tangent line to the curve (Don't understand)

3. The line through the origin with slope -1 is tangent to the curve at point P. Find the x and y coordinates at point P. (Also don't understand)

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Here is the second question:

Ship A is traveling due west toward Blunt Rock at a speed of 15 km/hr. Ship B is traveling due north away from Blunt Rock at a speed of 10 km/hr. Let x be the distance between Ship A and Blunt Rock at time t, and let y be the distance between Ship B and Blunt Rock at time t.

1. Find the distance, in km, between Ship A and Ship B when x=4 km and y=3 km (seems simple, use pythagorean theorem to get hypotenuse = 5 km)

2. Find the rate of change, in km/hr, of the distance between the two ships when x=4km and y=3km. (Think I got this, using implicit on pytahgorean theorem I get -6km/hr)

3. Let theta be the angle [at ship A, between the x axis and hypotenuse]. Find the rate of change of theta, in radians per hour, when x=4km and y=3km. (Not sure how this is done)

Thank you in advance