It takes 26.8 ml of a 0.0700 m naoh standard solution to neutralize a 250 ml sample of lactic acid (c3h6o3). what mass of lactic acid was dissolved in the sample?

There is 1 OH- in 1 molecule of NaOH. 
Also, there is 1 H+ in 1 molecule of lactic acid.

So the reaction is simple.
so just equate the moles
moles of OH- in NaOH = moles of H+ in lactic acid
26.8 x 0.07 = 250 x Mole of lactic
Moles of lactic = 0.0075

so mass = 0.0075 x 90.8 =  0.681 g

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .