How do i solve this algebra equation x+7=2x-8

Find the slope of the line below . enter your answer as a fraction or decimal. use a slash mark ( / ) as the fraction bar if necessary

Which one ? is the answer and how to find this answer

The birth weights of newborn babies in the unites states follow in a normal distrubution with a mean of 3.4 kg and standard deviation of 0.6 kg. reaserches interested in studying how. children gain weights decide to take random samples of 100 newborn babies and calculate the sample mean birth weights for each sample