Why the answer is 50 which is A

Price Demand schedule for tennis Price Demand schedule for tennis per hour lesson of adults per hour lesson of children $30 $30 Quantity in hours Quantity in hours Refer to the graph above to answer this question. The graph shows a tennis coach charges $20 per hour for tennis lessons for adults and $10 per hour for tennis lessons for children. Suppose the coach provides lessons to the children only. What is the amount of the consumer surplus of the children taking the tennis lessons? -A) $50. O B) $20. x . C) $120. OD) $160. OE) Cannot be determined