Before I changed my phone plan, I was paying 88 yuan per month. After that, I switched to a plan that costs 39 yuan per month. Currently, I only need to pay 30 yuan per month for my plan. The plan includes 5GB of data traffic and 100 minutes of call time. In reality, my data usage rate is less than 30%, and I rarely use up the full amount. I am a mobile phone user. How much do you need to pay for your monthly mobile phone bill?