To find the relationship between hours of work and the pay, I divided the total paycheck given by the 25 hours of work, which got me what a 25th of that paycheck would be, which represents what you would earn in an hour with a flat rate.
312.50 / 25 = 12.5
Check:
12.5 * 25 (hours of work) = 312.50 (Given total paycheck)
That's how we know the pay per hour, which is the relationship between t and p.