I really don't understand how I can evaluate this help

The mean temperature for the first 4 days in january was 7°c. the mean temperature for the first 5 days in january was 5°c. what was the temperature on the 5th day?

Cherie measures and records the lengths and sizes of the same style of a sandal found at a shoe store. which equation can be used to determine the approximate shoe size, s, for a foot length of x inches? s = x – 2 s = 2x – 10 s = x + 6 s = 2x + 4

Find the exact value of each of the following. in each case, show your work and explain the steps you take to find the value. (a) sin 17π/6 (b) tan 13π/4 (c) sec 11π/3