How do I subtract a mass of numbers from a number?

Probably a super simple one but I'm stuck


A1 245
A2
A3 8
A4 7
A5 90
A6 15
A7 67
A8 13

A1 being the Total
A2 I want to be the difference whether it be plus or minus, of A1 minused A3-A8,
in this case 45 is the answer

Thanks!