Look at the series: 58,52, 46, 40, 34, ……, what number should come next?

This is a simple subtraction series. 

Each number is 6 less than the previous number.

(58 – 6 = 52) (52 – 6 = 46) (46 – 6 = 40) (40 – 6 = 34)

(34 – 6 = 28)

So the answer is b = 28.