p denotes price of a single gum ball. So from question stem, we get:
gp = 4.5

single equation, two unknowns: cannot isolate p.

Stat. (1) translates into g(p+2) = 4.5*140%.

gp+2g = 4.5*7/5.
That's another equation with g and p. If number of different equations equals number of unknowns, it is possible to solve for the unknowns and find g and p. Stat. (1) is sufficient.

Stat (2): g(p-1) = 4.5-0.9
gp-g = 3.6
Again, two equations with two unknowns is sufficient.

answer is D, unless I'm missing something particularly nasty or far-fetched.