Let the rate of interest be x% per year and the time period be x years.

Simple interest = (Principal * Rate * Time) / 100

According to the problem,

Simple interest = Rs. 432 Principal = Rs. 1200 Time = x years Rate = x%

Substituting these values in the formula, we get:

432 = (1200 * x * x) / 100

Simplifying this equation, we get:

43200 = 1200x^2

Dividing both sides by 1200, we get:

x^2 = 36

Taking the square root of both sides, we get:

x = 6

Therefore, the rate of interest is 6% per year and the time period is also 6 years.