Plsss help explain I have an exam later and I need to understand this

Graph the line with the given slope m and y-intercept b. m=-3,b=1

Solve for b. ab + c= d b= a + old ob=allc-ch b= (d-c/a

Masons cell phone company charges $0.12 for every text message he sends plus $2.50 per month if mason sent 25 messages this month how much money does he owe the one with the correct answer and explanation gets 10 points and is marked as the brainliest answer