Simplify the sum or difference -6√10+5√90
a. 9√10 (correct answer)
b. -9√10
c -39√10
d - 10

A.

Step-by-step explanation:

The given expression is  

Remove the perfect square from the second radical.

This implies

The correct choice is A

d. millimeters per hour.

step-by-step explanation:

we are given that,

carlo used a rain gauge to measure the amount of water his lawn is receiving from the sprinklers.

since, according to the options, we see that,

water cannot be measured by 'miles per hour', 'meters per second' and 'grams per seconds'.

we get that, the water can be measured by 'millimeters per hour'.

hence, the appropriate rate for describing the amount of water is 'millimeters per hour'.