1. 15 * (a — 4) = 42 + 8 * (a — 4)
15a — 60 = 42 + 8a — 32
15a — 8a = 10 + 60
7a = 70; a = 10;
2. (y + 1) * 18 = 36 + 12 * (y + 1)
18y + 18 = 36 + 12y + 12
18y — 12y = 48 — 18
6y = 30; y = 5;
3. (k + 5) * 7 — 54 = (k + 5) * 4
7k + 35 — 54 = 4k + 20
7k — 4k = 20 + 19
3k = 39; k = 13;
4. 17 * (c — 2) — 36 = 19 + (c — 2) * 12
17c — 34 — 36 = 19 + 12c — 24
17c — 12c = —5 + 70
5c = 65; c = 13.