AP bio experts, help!!!?!?

The base height of the dingdong plant is 10cm. 4 genes contribute to the height of the plant, and each dominant allele contributes 3cm to height. If you cross a 10cm plant(quadruply zygous recessive) with a 34cm plant, how many pheotypic cles will be in F2? ( please show steps<3) choices: 4, 8, 64, 5, 9