Answer
The equation for the amount of drug received on the 7th day in terms of u and d is
a₇ = u + 6d
Step-by-step explanation
The description of the amount of drug administered on the first day and how the amount increases each day by d shows that this is an arithmetic progression question.
For an arithmetic progression with first term, u, and common difference, d, the nth term is given as
aₙ = u + (n - 1) d
a) So, for the 7th day
a₇ = u + (7 - 1) d
a₇ = u + 6d
Hope this Helps!!!