When were double replacement reactions discovered

Mike and mitchell decide to have a foot race. they mark off a stretch of 100 yards, and recruit cindy to work the stopwatch. after running the race and looking at the results, cindy declared that mitchell was the fastest. so how did the boys times compare?

What substance has a mass of 9.5g and volume of 2.1cm^3

Use the de broglie's wave equation to find the wavelength of an electron moving at 4.5 × 106 m/s. show your work. note: h= plank's constant (6.62607 x 10-34 j s)