Explanation:
well, 9 is in the place of thousands.
0 is in the place of hundreds.
0 is in the place of tens.
2 is in the place of single units.
0 is in the place of tenths.
5 is in the place of hundredths.
remember, fractions like 1/x are expressed as negative exponents, like x^-1 for 1/x.
the same applies to tenths, hundredths, thousandths, ... as e.g. hundred = 10², hundredth = 10^-2
and an exponent of 0 like x⁰ always turns the number to 1. x⁰ = 1 for any x.
so, our number is
9×10³ + 0×10² + 0×10¹ + 2×10⁰ + 0×10^-1 + 5×10^-2 =
9×10³ + 2×10⁰ + 5×10^-2
a = 0, b = -2