i)A mortgage of $80,000 is taken out on a property and to be repaid over 25 years. Using this equation find monthly repayments $x.
80000(1.07)^25 - 12x(1+1.07+.107^2 + ... +1.07^24).
ii)Calculate as percentages how much of the original mortgage is paid off in each of the first two years.
Your given equation makes no sense in terms of monthly payments.
Your problem does not contain any information about the rate of interest, but from
the "formula" stated in ... (1.07)^25 .., I would say there is an annual rate of 7% for 25 years, but without any reference to compounding.
See if you can fix your post and I will take a look at it