In pythagorean theorem a^2 and b^2 are always the two sidies that aren't the hypotenuse, so line b can be found by inputting the values of a and c (or you can substitute b instead of a, but it doesn't matter); line DC is the hypotenuse.
3^2 + b^2 = 5^2
9 + b^2 = 25
subtract 9 on both sides
b^2 = 16
square root on both sides
b = 4
now that we know the value of line b is 4, we can use the pythagorean theorem on triangle ABD.
7^2 + 4^2 = c^2
49 + 16 = c^2
65 = c^2
square root both sides
square root of 65 is 8.0622577483
rounded to nearest hundredth 8.062
