Triangle abc is an equilateral triangle with side lengths of 10 inches. what is the length, in inches, of ad?

The height of an equilateral triangle is found by the formula:
height = (sq root (3) / 2 ) * side length
height = ( 1.7320508076  / 2) * 10
height = (  0.8660254038 ) * 10
height = 8.660254038 inches     

1.17+3.99a. you combine the terms with a to create 3.99 and the 1.17 stays because it has no like terms or a variable