Answer:
4, based on the assumption that the R allele is dominant over the r allele, and that the T allele is dominant over the t allele.
Step-by-step explanation:
Any bush with a dominant petal color allele (R) will have red petals. This includes Rr and RR.
Any bush with a dominant bush size allele (T) will have a tall bush. This includes Tt and TT.
The only way to acquire a short bush or pink petals is to have two recessive alleles together (tt, rr).
RRTT, RrTT, RRTt, and RrTt -> red petals with tall bushes
RRtt, Rrtt -> Red petals with short bushes
rrTt, rrTT -> pink petals and tall bushes
rrtt-> pink petals with short bushes.
These are the four phenotype variations possible in this dihybrid cross.