It's Algebra I, 9th grade, so please make it easy

15. MODELING WITH MATHEMATICS The altitude a (in feet) of a plane t minutes after liftoff is given by a = 3400t + 600. How many minutes after liftoff is the plane at an altitude of 21,000 feet? 16. MODELING WITH MATHEMATICS A repair bill for your car is $553. The parts cost $265. The labor cost is $48 per hour. Write and solve an equation to find the number of hours of labor spent repairing the car. USING TOOLS In Exercises 25-28, find the value of the variable. Then find the angle measures of the polygon. Use a protractor to check the reasonableness of your answer. 25. 26. 2k 45 2a Sum of angle MaMaA measures: 180 21sllob joy nerw Sum of angle 9 19q measures: 360 27. 28. 120 100 (6 + 45) xo 120 (2b - 90) 90 120 (x + 10) Sum of angle Sum of angle measures: 540 measures: 720 In Exercises 29-34, write and solve an equation to find the number. 29. The sum of twice a number and 13 is 75. 30. The difference of three times a number and 4 is -19. 31. Eight plus the quotient of a number and 3 is -2. 32. The sum of twice a number and half the number is 10. 33. Six times the sum of a number and 15 is - 42. 34. Four times the difference of a number and 7 is 12. USING EQUATIONS In Exercises 35-37, write and solve an equation to answer the question. Check that the units and 5.) on each side of the equation balance. (See Examples 4 35. During the summer, you work 30 hours per week at a gas station and earn $8.75 per hour. You also work as a landscaper for $1 1 per hour and can work as many hours as you want. You want to earn a total of $400 per week. How many hours must you work as a landscaper? 36. The area of the surface of the swimming pool is 210 square feet. What is the length d of the deep end (in feet)? deep shallow end end 10 ft d 9 ft