Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr * PpRr are expected to have white flowers and wrinkled seeds?

When crossing alleles for color, you get

25% pp

50% Pp

25% PP

White flowers are recessive, so there is a 1/4 chance

And when crossing alleles for shape you get

25% rr

50% Rr

25% RR

Wrinkled seeds are recessive so there is a 1/4 chance

Since you are looking for white flowers AND wrinkled seeds, you need to multiply 1/4 x 1/4, giving you a 1/16 chance that the offspring will have these two traits