What is the probability of an offspring inheriting to the recessive trait if its parents are both heterozygous?

For this you would use a punnet square (ill try my best to show it while typing)

heterozygous means different, so you have parents with alleles shown as Dr (D=dominate, r = recessive) since they cant have 2 dominate alleles.

D r

D Dr Dr

r Dr rr

to get the recessive trait you must have an allele shown recessive homozygous

since there are only 1 pair shown as rr out of 4 possibilities you'd have 1/4 which is 25%

25%