Answer:
She should invest 6976.74 $ principal on daughter's 12th birthday.
Explanation:
We have I = prt, where I represents simple interest, p represents principal, r represents interest rate, and t represents time in years.
Here p + I = 12,000 $
So, I = 12000-p
Interest rate r = 12% =0.12
Number of years = 18 - 12 = 6 years.
Substituting
12000-p = p x 0.12 x 6
p + 0.72 p = 12000
1.72 p = 12000
p = 6976.74 $
So, she should invest 6976.74 $ principal on daughter's 12th birthday.
