The given scenario corresponds to stratified sampling because the population is divided in to two strata and from each stratum a random sample of 50 teacher is selected. The stratified sampling involves the selection of random sample of sampling units from the strata constructed by dividing diverse population into similar groups. Here. in the given statement the population is "High School Teachers" which is divide into two strata "Male high school teacher" and "female high school teacher" and then selecting a random sample of size 50 from each stratum.
Hence the given situation corresponds to Stratified Sampling.
You would use the distributive property with the negative. So the second x becomes negative, but since the 7 is already negative it becomes positive. Think of it as if you put the two dashes together you can make a plus sign.
