How do you draw a tetrapeptide from the one letter codes(Amino acids) and also give the pI, if given the pKa values?

Question

For example the Amino acids: S,T,G,L

i need some guidance, so i just look up the codes and draw them attached to each other form n-terminus to c-terminus. and to find the pi doe i just average the pka values?

any help would be helpful..