Please answer, not hard at all. 10 points

(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

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).

3x + 4y = 5 x- 3y = -7 solve by substitution