What is the answer to 2x + 21

(note i put the graph in so plz )the graph shows the amount of water that remains in a barrel after it begins to leak. the variable x represents the number of days that have passed since the barrel was filled, and y represents the number of gallons of water that remain in the barrel. what is the slope of the line

What are the measures of ∠a, ∠b, ∠c and ∠d? explain how to find each of the angle measure.

If m 17 27 90 63 ** picture is attached