D, hope this is right! :)
Answer: 2 hr.
Explanation: Think back to rate of change. <em>d</em> = <em>rt</em>, <em>r</em> = <em>d/t</em>, <em>t</em> = <em>d/r</em>. In this case, we will be using <em>d</em> = <em>rt</em>. Mph would be <em>r</em>, rate, so you would categorize 15 mph and 8 mph under rate. <em>t</em> should represent the time each cyclist traveled. Tracey's and Emma's distance, <em>d</em>, would be the same as their mph, hence Tracey's being 15<em>t</em> and Emma's would be 8<em>t</em>. When you add Tracey's distance plus Emma's distance, you end up with 46 mi. Now, you need to combine like terms, which should look like 15<em>t</em> + 8<em>t </em> = 46. Add 15 and 8 to get 23, so it should be 23<em>t</em> = 46 now. Then, divide both sides of the equation by 23 and now you should have your answer, <em>t</em> = 2 hr.
If a number has a decimal that is .5+, you round up. If it is .4-, you round down. So 817.502 would be 818.
