Explanation:
equal steps.
so, starting at -2 the fifth number (= after the 4th step) is 26.
so, the interval is 26 - -2 = 28 long.
28/4 = 7
so, each step is 7 long.
the third number is after the second step, that means after adding 2×7 = 14
-2 + 14 = 12
12 is the third number.