Answer:
5%
Step-by-step explanation:
Let the interest rate be x100
So we have for simple interest: x100×$2600=$390
This is the same as: ddddddddddx×$2600100=$390
x×$2600100=$390
Divide both sides by $26.
x×$26$26=$390$26
x×1=$390$26
x=15
But x is from x100
The % symbol is like a unit of measurement and one that is worth 1100
So 15100d→d15×1100d→d15×%→15%
But this is over 3 years so the annual interest rate is d15%3=5%