Two different experiments are conducted to study the growth of bacteria. In Experiment A, the number of bacteria $N_A$ after $t$ hours is given by $N_A=500(1.05{)}^t$. In Experiment B, the number of bacteria $N_B$ after $t$ hours is given by $N_B=200(1.10{)}^t$. What is the positive difference between the initial number of bacteria in Experiment A and Experiment B?