Please help with these questions.

11. A snowball melts so that its surface area decreases at a rate of 0.5 cmzr'min. Find the rate at which the radius decreases when the radius is 4 cm. (SA=4:rrZ) (4 marks) 12. Brent is driving west at 60 kmlh and Aaron is driving south at 70 kmlh. Both cars are approaching the intersection of the two roads. At what rate is the distance between the cars decreasing when Brent's car is 0.4 km and Aaron's is 0.3 km from the intersection? (4 marks) 13. Awater tank at a ltration plant is built in the shape of an inverted cone with height 5.2 m and diameter 5 m at the top. Water is being pumped into the tank at a rate of 1.2 malmin. Find the rate at which the water level is rising when there is 811 m3 of water. (4 marks) 14. For the function f (x)=ax3+bx25x+9 , determine the values of a and b so that f(1)=12 and f'(1)=3. (4 marks) 15. Determine the equations of two lines that pass through the point (-1,-3) and are tangent to the graph of y=x2+1. (8 marks) 16. Two particles have positions at time t given by S. =4! -tz and S; = 512 43. Find the velocities V1 and v2 at the instant the accelerations of the two particles are equal.