Testing between two means (2)

Each of the eight items was valued independently by an antique dealer and an antique expert. The valuations, in thousand of dollars, are shown below.

Item------- 1-----2-----3-----4-----5-----6-----7------8
Dealer---875--575--970--425--460--255--1050--350
Export---685--510--775--355--540--195--825---425

(a) Carry out the appropriate test at 5% level of significance to investigate the claim that the dealer's valuations are, on average, greater than the expert.
(b) State the necessary assumption required for (a).