You go from left to right and tell what each numeral represents write it as a factor of 10.
The 1 is "one ten" because it is in the 10's place
We can write that as 1 x 10¹
The 2 "two ones" which can be written as 2 x 10⁰ (anything to the zero power is 1)
Negative powers of 10 will help us with the decimals
The 5 is "five tenths" or 5 x 10⁻¹
The 7 is "five hundredths" or 7 x 10⁻²
Finally the 6 is "6 thousandths" or 6 x 10⁻³
Final answer in expanded form is:
1 x 10¹ + 2 x 10° + 5 x 10⁻¹ + 7 x 10 ⁻² + 6 x 10⁻³