How do I get to -11 to -5

How do i do this activity, is appreciated

Which shows the first equation written in slope-intercept form? 1/2 (2y + 10) = 7x

If a distance of 75 yds is measured back from the edge of the canyon and two angles are measured , find the distance across the canyon angle acb = 50° angle abc=100° a=75 yds what does c equal?