Answer:
6.5
Explanation:
This triangle has a right-angle, therefore it is a right-triangle. This means we can apply the Pythagorean Theorem:

a and b are the short sides, and c is the long side, called a hypotenuse
We know one side length (3.6) and the hypotenuse (7.4). We can plug these values into the equation.

To round to the tens place we look at the digit in the hundredths place. Because it is 6, we round 6.465... to 6.5