Can you please help me (without using a calculator)

Jenisey has $24 to spend on seven pencils. after buying them she had $10. how much did each pencil cost.?

Solve for x and y: 217x + 131y = 913; 131x + 217y = 827

Cody started biking to the park traveling 15 mph, after some time the bike got a flat so cody walked the rest of the way, traveling 4 mph. if the total trip to the park took 6 hours and it was 46 miles away, how long did cody travel at each speed? solve using rate times time= distance