First image the measure of the hypotenuse is :

second image the length of the unknown leg is:

These are right triangles, which means you can use the Pythagorean Theorem to find the hypotenuse and unknown leg. The Pythagorean Theorem:

a^2 + b^2 = c^2, where c is the hypotenuse.

7^2 + 24^2 = c^2
49 + 576 = c^2
625 = c^2
25 = c

The length of the hypotenuse is 25 units.

To find the length of the unknown leg, you substitute values as they are given to you:

a^2 + 24^2 = 26^2
a^2 + 576 = 676
a^2 = 100
a = 10

Answers:
c = 25
a = 10

Hope this helps!