Unsure how much to charge for dog sitting

I’m new to dog sitting. I do have experience with dogs, I‘ve owned many myself my entire life. I’ve now got the opportunity to dog sit, their requirements are 2 drop in visits in the morning and night, 2 walks in the morning and evening for 2 small dogs. How much should I charge them per day? They want me to look after them for 5 days while on holiday, I’m from the UK.