V.- the same number each 2 missing from the sequence v v i.

We have an artihmetic progression:
an=a₁+(n-1)d
an=Nth term of the series
n=total numbers of  terms in the series
d=difference between two succesive numbers

In this case
a₁=7
a₄=-5

a₄=a₁+(4-1)d
a₄=7+3d
-5=7+3d
3d=-5-7
3d=-12
d=-12/3
d=-4

We have to calculate a₂ and a₃
a₂=7+(2-1)(-4)=7-4=3
a₃=7-(3-1)(-4)=7-8=-1

7      3      -1     -5

Yes you do, so £1973.09 - £1473.50 = £499.59 so tim overpaid £499.59 .hope this ; )