H = P * a^ t

p- will be equal to 125
a- will be 3^
t- will be 4 years

so how many Homes' will be built for H in 4 years, how do I write this formula

H = p a^t

H = 125 * 3^4

= 125 * 3*3*3*3

= 125 * 81

= 10,125

However your formula does not make sense to me. I suspect a typo. In real life you would not build three times as many homes every year as in the year before. We would run out of planet very quickly.