a.) The phenotype is yellow, smooth
This is because (Y) yellow is dominant over (y) green. If an organism has a trait that is dominant, it will show up with no exceptions (YY, Yy, Ss, SS). Recessive traits on the other hand will only show up if both the maternal (Mom) and the paternal (Dad) copy given are both recessive (yy or ss).
b.) It depends on what the YySs plant is paired with. Will it be paired with another YySs, with YYSS, yyss, YySS, yySS, YYss...? For example, if it is paired with another YySs, make a punnett square.