题目

We work with Cambridge County Council's Participation Team to create opportunities for young people to visit the University and learn more about it. The following events are scheduled for the 2019/2020 academic year.SuperStar workshops12 workshops are planned for young people aged 7 to 11. These half-day visits will be held throughout the year, at times when young people are not at school. If participants complete 8 of the 12 workshops, they will be awarded the nationally recognized SuperStar Crest Award.Please note, workshops will only run if we have a sufficient number of attendees (usually 4．80g15%的硝酸钠溶液中，加入20g硝酸钠全部溶解，求此硝酸钠溶液中溶质的质量分数？若又想将溶液恢复到原来的浓度，需要加水多少克？