Can you help me with this one pls

Chlorophyll a had the molecular formula c55h72mgn4o5 how many atoms are in this molecule

A40 kilogram skier starts at the top of a 12 meter high slope. at the bottom, she is travelling 10 meters per second. how much energy does she lose to friction

Tooth enamel consists mainly of the mineral calcium hydroxyapatite, ca_10(po_4)_6(oh)_2. trace elements in teeth of archaeological specimens provide anthropologist with clues about diet and diseases of ancient people. students at hamline university measured strontium in enamel from extracted wisdom teeth by atomic absorption spectroscopy. solutions with a constant total volume of 10.0 ml contained 0.726 mg of dissolved tooth enamel plus variable concentrations of added sr. added sr find the concentration of sr in the 10 ml sample solution in parts per billion = ng/ml. find the concentration of sr in tooth enamel in parts per million = mu g/g.