Explanation:

To understand the expression 3 x 10^-5, we need to understand scientific notation. Scientific notation is a way of expressing very large or very small numbers in a concise and convenient manner.

In scientific notation, a number is written in the form a x 10^b, where a is a number between 1 and 10, and b is an integer that represents the power of 10.

In the given expression, 3 x 10^-5, the base number is 3 and the exponent is -5. This means that we need to multiply 3 by 10 raised to the power of -5.

To calculate this, we can use the following steps:

Step 1:
Write down the base number, which is 3.

Step 2:
Write down 10 raised to the power of the exponent, which is -5. Since the exponent is negative, we need to take the reciprocal of 10 raised to the positive exponent. In this case, 10^-5 is equal to 1/10^5.

Step 3:
Multiply the base number by the result from step 2. In this case, 3 x (1/10^5).

Step 4:
Simplify the expression. 3 x (1/10^5) can be written as 3/10^5.

Step 5:
Express the result in decimal form. To do this, we can rewrite 10^5 as 100,000. So, 3/10^5 is equal to 3/100,000.

Therefore, the usual form of the expression 3 x 10^-5 is 0.00003, which is option 'A'.

Summary:
The expression 3 x 10^-5 is written in scientific notation. To convert it to usual form, we need to multiply the base number by 10 raised to the power of the exponent. In this case, 3 x 10^-5 is equal to 0.00003.

0.000003