March 2020 is considered for the year 2019.
pg. 32
"Our gender pay gap data in March 2020 for the group showed females were paid 1.7% more than males, using the median results, and males 10.4% more than females, using mean results (male average pay being higher due to a greater proportion of males in the most senior roles), which is significantly below the national average as reported by ONS. Importantly, 45% of our senior team are female."
The company states that male employees were paid 10.4% more than females employees as per mean gaps results and females were paid 1.7% more than male employees according to median pay gap results. The median pay gap is considered here.
This question is asking for the mean. Therefore 100 - 10.4 = 89.6