Free points willing to give!

(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

Find the value of x for which the lines are parallel.

Ten times the square of a non-zero number is eqaul to ninety times the number