algebra 1 question

Question

 A firefighter spraying water on a fire student on the middle rung of a ladder. The smoke lessened, so she moved up 3 rungs. It got too hot, so she backed down 5 rungs. Later, she went up 7 rungs and stayed until the fire was out. Then, she climbed the remaining 4 rungs and went into the building. How many rungs does the ladder have 

Answer 1

r/2 + 3 - 5 + 4 + 7 = r

r/2 + 9 = r

9 = r/2

r = 18