Answer:
$5136
Step-by-step explanation:
The balance in Ethan's account is multiplied in t years by the factor ...
(1 +r/12)^(12t) . . . . . where r is the interest rate
We want to find the time t when this factor is 2 and r = 0.0525
2 = (1 +0.0525/12)^(12t)
log(2) = 12t·log(1.004375)
t = log(2)/(12·log(1.004375))
t ≈ 13.2317 . . . years for Ethan's money to double
__
The value of Stella's account is given by ...
A = P·e^(rt)
Stella's interest rate r is 0.0575, and we want to use the value of t from above.
A = 2400(e^(0.0575×13.23167)) ≈ 2400(2.140032) ≈ 5136.076
Stella will have about $5136 in her account when Ethan's money has doubled.
