Believe it or not (#1) Mystery Cache

The cache is not at the published coordinates - these are for our local secondary school which did a pretty decent job getting the kids through GCSE Maths...

Consider the solutions, x₁ and x₂ (where x₁>x₂), to the quadratic equation, x²-7x+10=0.

Now, if it is to be demonstrated that x₂+x₂=x₁, determine the time (t) and the place (p).

The cache can be found at:
N 51° A.B W 000° C.D

where:
A=9*x₂
B=(t/2)-163
C=7*x₁
D=(6*p)+21

NB. The chap in the inset, above, is David Smith - headmaster from 2001 to 2013. (I wasn't consulted about his departure).

Congratulations on the FTF to Kermit&Co and clarkester.