Below is the formula for calculating monthly payments for a fixed-rate loan. M equals P times the fraction with a numerator of i times the quantity 1 plus i end quantity to the power of n times t all over the denominator of the quantity 1 plus i end quantity to the power of n times t end power minus 1 end fraction

Part 1: Explain what the following variables represent and how changing each one affects the monthly payment amount: P, i, and t.
Part 2: Explain how changing each variable (P, i, and t) affects the total cost of principal and interest over the life of the loan.