Yohanna is conditioning all summer to prepare for her high school's varsity soccer team tryouts. She is incorporating walking planks into her daily training plan. Every day, she will complete four more walking planks than the day before. Yohanna starts with five walking planks on the first day. Write an explicit formula that can be used to find the number of walking planks she completes on any given day. Use the formula to calculate the number of walking planks Yohanna will do on the 12th day?