Help please, I don’t understand

Answer:
v = 16.155 m/s
Step-by-step explanation:
[tex]W = 0.5 mv^2 \\ plug \: m = 6 \: and \: w = 783 \\ 783 = 0.5 \times 6 \times {v}^{2} \\ 783 = 3 {v}^{2} \\ {v}^{2} = \frac{783}{3} \\ {v}^{2} = 261 \\ v = \sqrt{261} \\ v = 16.1554944 \\ \huge \red{ \boxed{v = 16.155 \: m {s}^{ - 1} }} \\ [/tex]