In the beginning, there is a solution in the tank which consists of 80% water and 20% salt by weight, totaling 350kg. At any moment, a 30% salt solution by weight is being fed into the tank at a rate of 12kg/min. The outflow rate is 10kg/min. Using the Euler method, calculate the percentage of salt in the tank after 20 minutes. Take t as 4 minutes.

Xn+1 = Xn + (dX/dt)n t tn+1 = tn + t