charlie runs at a speed of 3 yards per second about how many miles per hour does chasrlie run ?

3 yds. = 9 ft

So we have

9 ft/sec * 3600(secs in one hr) / 5280(feet in one mile)  ≈  6.14 mph

$$\frac{3\;yards}{sec}*\frac{60\; secs}{min}*\frac{60\;mins}{hour}*\frac{0.000568182\;mile}{yard} = \mathbf{6.1363656\;\frac{miles}{hour}}.$$