Answer:
f=8
Step-by-step explanation:
Step 1-
All triangles have interior angles equal to 180, so with this knowledge, we can do:
180-40-30=110
Step 2-
Knowing that 110 is equal to S, we set it equal in an equation and solve
(13f+6)=110
Subtract 6 from both sides to get rid of it
13f=104
Divide 104 by 13 to get rid of it
f=8
Hope this helps!