Ranjit goes to mathematics lectures and physics lectures. The length, in minutes, of a mathematics lecture is modelled by the variable $X$ with distribution $N\left( {36,{\text{ }}{{3.5}^2}} \right)$. The length, in minutes, of a physics lecture is modelled by the independent variable $Y$ with distribution $N\left( {55,{\text{ }}{{5.2}^2}} \right)$.

a) Find the probability that the total length of two mathematics lectures and one physics lecture is less than 140 minutes. 

b) Ranjit calculates how long he will need to spend revising the content of each lecture as follows. Each minute of a mathematics lecture requires 1 minute of revision and each minute of a physics lecture requires $1\frac{1}{2}$ minutes of revision. Find the probability that the total revision time required for one mathematics lecture and one physics lecture is more than 100 minutes.