There's an error in the question: sin(a)=24cos(a)/7.
Then, tan(a)=24/7 so we can draw a right triangle with hypotenuse=√(242+72)=√625=25.
Therefore, sin(a)=24/25, cos(a)=7/25, sec(a)=25/7, and:
14tan(a)=14(24/7)=48; 25cos(a)=7; -7sec(a)=-25.
Adding these we get: 48+7-25=30 QED