library(deSolve)

bank_deriv <- function(t, y, parms) {
  with(as.list(c(y, parms)), {
    dB <- r * B
    list(c(dB))
  })
}

# Parameters
parms <- c(r = 0.05)   # 5% annual interest
y0 <- c(B = 1000)      # initial balance = 1000
times <- seq(0, 10, by = 0.1)  # simulate 10 years

out <- ode(y = y0, times = times, func = bank_deriv, parms = parms)

plot(out, main = "Bank Balance with 5% Interest (deSolve)")