Answer:
Step-by-step explanation:
-9 because a negative plus a negative is a negative so -5+-4 or -5-4 is -9
Answer:

Step-by-step explanation:
Red blood cell: 
Grain of sand: 
The "how many times larger" part can be figured out by forming a ratio between the two diameters above:

Note that dividing the powers of ten corresponds to subtracting the denominator power from the numerator power of 10.