Can someone help me with this please

what is the area of the circle if xy=5.4mm?

Stoichiometry- i need with 14 and 15! an explanation would be appreciated!

Sand is more likely than shale to preserve fossils. true false

Calculate the h3o+ concentration in a solution of acetic acid if the concentration of molecular acetic acid present at equilibrium is 9.97x10-3 m and k for the dissociation is 1.86x10-5. ch3cooh(aq)+h2o(l)+> h3o+(aq)+ch3coo-(aq) show me how to get the answer.