Since tea and coffee sales are independent the joint distribution of their sold amounts in a minute is the product of their individual distributions.
Coffee sales are Poisson w/mean $\lambda_c=1.5$
Tea sales are Poisson w/mean $\lambda_t=0.5$
So the Joint PMF is given by
for (i) simply plug (1,1) in for (c,t)
for (ii) just recast things to be over the course of 3 minutes rather than 1.
Coffee sales are now Poisson with $\lambda_c=3*1.5=4.5$
Similarly Tea sales are now Poisson with $\lambda_t=1.5$
You should be able to finish from here.