You would multiply 12.50 by 4 because thats how much each lesson is and you go 4 times a month. You then multiply this by 12 because there are 12 months in a year. The answer comes out to $600 a year. Hope this helps. XD
Using the Pythagorean theorem (a² + b² = c²) you would end up with an equation like this: 36 + 64 = 100. You would then square root 100 and the answer would be 10 ft