Exterior angles are complementary to the opposite interior angle
For example:
x+2y=7
6x+7y=2
__________
x=7-2y *
6*(7-2y)+7y=2 **
__________
x=7-2y
42-12y+7y=2
__________
x=7-2y
-5y=-40
__________
x=7-2y
y=8
x=-9
In the second quadrant, both cos and tan are negative while only sin is positive.
To find tan, we will use the following property below:

Sec is the reciprocal of cos. If cos is a/b then sec is b/a. Since cos is 2/3 then sec is 3/2

Since tan is negative in the second quadrant. Hence,

Answer
If Micael is 2 years older than sam and sam is 15 than than micael is 17