Question

what is the value of f?

Explanation:

Step1: Find vertical adjacent angle

The angle opposite the 70° angle (vertical angle) is also $70^\circ$.

Step2: Calculate sum of known angles

Add the 40° and 70° angles:
$40^\circ + 70^\circ = 110^\circ$

Step3: Solve for $f$ using straight line

Angles on a straight line sum to $180^\circ$:
$f = 180^\circ - 110^\circ$

Answer:

$70^\circ$