Employee Class 1 NIC

Good day,

I was reviewing question 55 – Sasha from the TAX UK Text and I didn’t understand how part b(i) and c(i) were calcuated.

Part b(i) showed that £60,000 was the gross income and £55,120 was the net taxable earnings for Sasha as an employee.

Part C(i) showed that the class 1 NIC was calculated on the entire £60,000 rather than the net taxable earnings of £55,120.

Can you explain this please? I was of the understanding that the liability is calculated on the net taxable earnings. Please help.