86.3 Chapter 4. Linear equations of the first order. Exercise 4a at page 56

86.3.1 problem 1
86.3.2 problem 2
86.3.3 problem 3
86.3.4 problem 4
86.3.5 problem 5 (i)
86.3.6 problem 5 (ii)
86.3.7 problem 6 (i)
86.3.8 problem 6 (ii)
86.3.9 problem 7
86.3.10 problem 8
86.3.11 problem 9
86.3.12 problem 10
86.3.13 problem 11
86.3.14 problem 12
86.3.15 problem 13
86.3.16 problem 14