The average height of maize plants in a population = 180 cm.
The narrow-sense heritability h2 = 0.5
The selected plants are 10 cm taller on average. The offspring produced by them will be as tall as the selected parents. So, the next generation plants would be 10 cm taller than the population.
h2 = 0.5
So, the height which is heritable would be 10 cm × 0.5 = 5 cm in each generation.
It was done for eight generations. So, the increase in the height of final generation would be 8×5=40 cm.
The height of the plants after eight generations of selection would be 180 + 40=229 cm.