Respuesta :

Start with 20
After 1 month, 20 * 2 = 20 * 2^1
After 2 months, (20 * 2) * 2 = 20 * 2^2
 After 3 months, (20 * 2^2) * 2 = 20 * 2^3
After x months: 20 * 2^x

2x+20, x being a month