To make u the subject we proceed as follows:
D=ut+kt²
subtract kt² from both sides
D-kt²=ut+kt²-kt²
This will give us:
D-kt²=ut
next we divide both sides by t
(D-kt²)/t=ut/t
this will give us
u=(D-kt²)/t
simplifying the above we get:
u=D/t-kt
Answer: u=D/t-kt