what is the equation of line a to find the slope? also please only answer if you know, im desperate and this is my only hope

Is this trying to find the area?

Do the math. she originally had 50 dollars on her gift card and she had 12 dollars left on her gift card after she finished her shopping spree. if you subtract 50 minus 12 you get thirty eight dollars as your answer. so therefore, ciara spent 38 dollars total o