#### Answer

a=7

#### Work Step by Step

The Pythagorean Theorem states that for a right triangle, $a^{2} +b^{2} = c^{2}$. Thus, we plug in the values given for a, b, or c, and then we use these values to find the missing value:
$a^{2} + 2.4^{2} =7.4^{2} \\\\ a^{2} + 5.76=54.76 \\\\ a^{2} =49 \\\\ a=7$