Answer: 6.9
Step-by-step explanation:
The square root of 36 is 6 and the square root of 25 is 5. 30 is in between 36 and 25 so the square root should be between 6 and 5.

=

Multiply both sides by 15
6 =

Multiply both sides by c
6c = 30 Divide both sides by 6
c = 5