How do i use the substitution method for these equations
y=3x+4
y=5x+12

Aladder that is 30 ft long needs to reach 27 ft up a building. what should the angle of the vertical be?

Diana is painting statues she has 7/8 of a liter of paint each statue requires 1/20 of a liter of paint how many statues can she paint?

Sanya noticed that the temperature was falling at a steady rate of 1.4 degrees every hour from the time that she first checked her outdoor thermometer. by 6 a. m., the temperature had fallen 21 degrees. which expression can you use to find how many hours earlier she had first checked the thermometer?