I'm supposed the quadratic formula for this but i don't understand it

The sport of curling is quite popular in Canada. A curler slides a 19.1-kg stone so that it strikes a competitor's identical stationary stone at 6.20 m/s before moving at an angle of 60.0 counterclockwise from its initial direction. The competitor's stone moves off at 5.40 m/s. Macmillan Learning Determine the final speed of the first stone v1,f. 1.27 Ulf = m/s Incorrect Determine the final direction of the second stone as an angle a relative to the first stone's initial direction of motion. Let 11.79 counterclockwise from the first stone's initial direction define a= the direction of positive angles. IncorrectAttempt 3 ikes a d Feedback X nitial di Your answer for U1,f is too large. You may have forgotten to divide by 2 when using the quadratic formula. Macmillan Learning The quadratic formula is as follows. If ax2 + bx + c = 0 and a # 0, then the following quadratic formula gives x. -b+ Vb2 - 4ac X = 2a Note that the denominator includes a factor of 2. Make sure to use the correct expression for the quadratic formula when solving quadratic equations