Answer:
a = 6, b = 8, and c = 10.
Step-by-step explanation:
You can easily use the Pythagorean Theorem to solve all of these.
a = 4; b = 6; c = 8... 4^2 + 6^2 = 16 + 36 = 52. 8^2 = 64. 52 is not equal to 64, so the first choice is not a right triangle.
a = 6; b = 8; c = 10... Well this is a multiple of the 3-4-5 Pythagorean triple, so this is a right triangle.
a = 5; b = 6; c = 761... 5^2 + 6^2 = 25 + 36 = 61. 761^2 = 579121, which is not equal to 61, so the third choice is not a right triangle.
a = 6; b = 9; c = 12... 6^2 + 9^2 = 36 + 81 = 117. 12^2 = 144, which is not equal to 117, so the fourth choice is not a right triangle.
The only case where there is a right triangle is the second choice, where a = 6, b = 8, and c = 10.
Hope this helps!