Question

For the first order reaction A → 3B + C, when [A]o = 0.015 mol/L, the concentration of B increases to 0.018 mol/L in 3.0 min.
a) What is the rate constant for the reaction expressed as rate loss of A? (Ans. k = 0.17 min-1)
b) How much more time would be needed for the concentration of B to increase to 0.030 mol/L (Ans. An additional 3.5 min)

Not getting any of those answers and I'm using 1st order integrated and the [a]/t=1/3[b]/t to figure it out but its not giving me those answers