C I’m not really sure but try
Answer:
I think it is 11 Feet
Step-by-step explanation:
You can perform all kind of operation that are one the inverse of the other, so that the value won't change. For example, you can multiply and divide by 2:

Or add and subtract 5:

5.7t < 420 divide both sides by 5.7
5.7 5.7
t < 73.68