Answer:
You do not count the zero to the left of the decimal
Explanation:
That zero is just a placeholder as there is nothing to the left of the decimal, you could also write the number as .000157
Your answer is correct, 0.000157 is 1.57x10^-4
Scientific notation is just expressing numbers in their exponential form. The power/exponent is found by counting how many times the decimal has moved to the right or the left.