An art supply cabinet contains a total of 75 charcoal pencils, oil pastel crayons, and sketchpads. Twice the number of oil pastel crayons is one more than the number of pencils. Four times the number of oil pastel crayons plus twice the number of pencils equals 8 more than 3 times the number of sketchpads. Write and solve a system of equations to determine the number of each type of these supplies in the cabinet.​