ElectricPavlov

Circumradius of equilateral triangle with side length 'a' is given by 

2 x  h/3   = a * sqrt (3) / 6 

Will has covered 45 minutes worth of lake distance  

       45 min  * 50 m/min = 2250 m meters before Grace starts ....so there is only   2800 - 2250 = 550 meters to cover before they meet 

               their closing rate is (50 + 30 )  = 80 m/min 

                              distance / rate = time 

                                         550 m / 80 m/min = 6 7/8 minutes they will meet after Gracie starts 

                  which would be   2:45 + 6 7/8  = 2:51  and 7/8 = 2:51 and 52.5 seconds  (almost  2:52 pm) 

Where they intersect, they are equal :

x^3 + x^2 -3x + 5   =  x^3 + 2x^2 

                            0 = x^2 +3x-5 

                                Use quadratic formula to find x = 1.193   and  -4.193 

                                           Use these values in either of the equations to find the corresponding y =  4.54   and -38.54