[STEP]Fill in $b=75$, $d=25$ and the opposite angles in the figure[/STEP]

[STEP]Calculate $c$ using the fact that the angle on a strait line is always $180^{\circ}$[/STEP]

Since the sum of angles on a strait line is always $180^{\circ}$, we have

$$25+c+75=180$$

[ANS]$c=180-25-75=80$ [/ANS]