Answer:
1.
[tex]19 - 4c = 17 \\ 4c = 19 - 17 \\ 4c = 2 \\ \\ { \underline{c = \frac{1}{2} }}[/tex]
2.
[tex]1.1x + 1.2x - 5.4 = - 10 \\ \\ 2.3x = - 4.6 \\ { \underline{ \: \: x = - 2 \: \: }}[/tex]
3.
[tex]c = 15n + 85 \\ 385 = 15n + 85 \\ 15n = 300 \\ { \underline{ \: \: n = 20 \: \: }}[/tex]