Is 2x+5x+1 equivalent to 7x+1 and also if u don’t know don’t answer

What's the difference between: x≥0 and nonnegative integer. ?

What is the value of x? enter your answer in the box. photo attached.

While scuba diving, rajeev dove to a depth of 12.6 feet below the surface of the water and then descended another 8.7 feet. what expression can be used to find rajeev's new position? 12.6 – 8.7 –12.6 – 8.7 –12.6 – (–8.7) 12.6 – (–8.7)