In the tri angles of a triangle angle B exceeds twice angle A by 15. Express the measure of angle C in terms of angle A.

The interior angle sum of a triangle is equal to 180
degrees.  Therefore, A + B + C = 180.

When we translate the
statement from words into an equation we have: B = 2A +
15.

We can substitute (2A + 15) for B into the equation to
get:

A + (2A + 15) + C =
180.

To solve for the equation in terms of C we need to
simplify, and then "move" everything to the right side of the equation as shown
below:

A + (2A + 15) + C =
180

3A + 15 + C = 180                    Combine like
terms

     - 15           - 15                    Subtract
15 from both sides

3A + C =
165

-3A          -3A                           Subtract 3A
from both sides

C = 165 -
3A

To double-check for correctness you may substitute the
new value for C into the equation:

A + (2A + 15) + (165 -
3A) = 180

180 = 180