Answer:
WRONG ALL
Step-by-step explanation:
3. Should be:

4. Should be:

I hope this helps you :)
Putting it like 7*t*s*3*r*t and multiplying like terms using the commutative property, we get 21*t²*s*r or 21rst²
You can put each into standard form to see whether they have the right value.
5.5·10⁴ = 55,000 ≠ 0.00055