NEED HELP WITH PART A and B!

For a first-order reaction, the half-life is constant. It depends only on the rate constant k and not on the reactant concentration. It is expressed as The half-life of a reaction, t1/2, is the time it takes for the reactant concentration [A] to decrease by half. For example, after one half-life the concentration falls from the initial concentration [A]0 to [A]0/2, after a second half-life to [A]0/4, For a second-order reaction, the half-life depends on the rate constant and the after a third half-life to [A]0/8, and so on. on. concentration of the reactant and so is expressed as t1/2=k[A]01 Part A A certain first-order reaction (A products) has a rate constant of 5.40103s1 at 45C. How long does it take for the concentration of the reactant, [A], to drop to 6.25 % of the original concentration? Express your answer with the appropriate units. X Incorrect; Try Again; One attempt remaining A certain second-order reaction (B products) has a rate constant of 1.50103 M1s1 at 27C and an initial half-life of 206s. What is the concentration of the reactant B after one half-life? Express your answer with the appropriate units