Answer: 9,000
Step-by-step explanation: there are 9 number options for the first digit and 10 for the other 3, so 9x10x10x10=9000
Answer:

Step-by-step explanation:
The expression in the square root should be greater than or equal to zero, because square root of a negative number does not give a real number.

Answer and explanation:
- 5 = b - 2.3 add 2.3 to both sides
+2.3 +2.3
- 2.7 = b
<span>-x^2=4
x = -2i and x = 2i
-------------------------------</span>