Question 1164148
the simple interest formula is i = p * r * n
p is the principal
r is the interest rate per time period
n is the number of time periods.


in your problem, p is 8000 and r is .02 and i is 400.
your time period is years.
formula becomes  400 = 8000 * .02 * n
simplify to get 400 = 160 * n
solve for n to get n = 400 / 160 = 2.5 years.
8000 * .02 * 2.5 = 400
that's your solution.
the money must be invested for 2.5 years.