15. (a) Evaluate: sin 80° cos 10° + sin 59° sec 31°   16. (b) Saloni deposited Rs.150 per month in her bank for eight months under the Recurring Deposit Scheme. What will be the maturity value of her deposit, if the rate of interest is 8% per annum and the interest is calculated at the end of every month?   17. (c) Find the mean of the following distribution:- Class Interval 0 - 10 10 - 20 20 - 30 30 - 40 40 - 50 Frequency 10 6 8 12 5