Genetics question on additive alleles

I have an exam on Monday in plant and animal genetics and I just wanted some help with a question on additive alleles thanks.
Three independently segregating genes (A,B,C) each with two alleles determine height in a plant. Each additive allele adds 2cm to a base height of 2cm.
(a) What are the heights expected in the F1 progeny of a cross between the two homozygous strains: AABBCC (14cm tall plants) X aabbcc (2cm tall plants)
(b) When an F2 generation is developed by crossing individuals from the F1 population (F1 X F1) what is the distribution of plant height among the progeny of this cross? The answer should include the proportion of individuals in each height class and the height of these individuals.
(c) What proportion of the F2 plants will have heights equal to the heights of the original parent plants?
(d) What proportion of the F2 plants will breed true for the height shown in the F1 plants?

Parents: AABBCC (14cm tall plants) X aabbcc (2cm tall plants) => no ratio in the F1

AaBbCc (8cm) plants each upper case gives 2 cm

Trihybrid genotypic ratio 1:6:15:20:15:6:1 comes from (P + q)^6 where P is upper case or dominant allele & q is lower case or recessive allele

(P+q)^6 = 1P^6 q^0 + 6P^5q^1 + 15P^4q^2 + 20P^3q^3 + 15P^2q^4 + 6P^1q^5 + 1P^0q^6

1 - all upper case - AABBCC = 1P^6 q^0
6 – 5 upper case 1 lower- 2AABBCc +2AABbCC +2AaBBCC - 6 P^5q^1
15 – 4 upper 2 lower - 4AABbCc+4AaBbCC+4AaBBCc+1AABBcc+1AAbbCC+…
20 – 3 each case - 8AaBbCc+2AABbcc+2aaBbCC+2AabbCC+2AAbbCc +2AaBBCc+2aaBBCc
15 – 4aaBbCc+4 AabbCc+4 AaBbCc+1AAbbcc+1aaBBcc +1aabbCC
6 – 2Aabbcc+2aaBbcc+2aabbCc
1 - all lower case - aabbcc