The raise was 5% which is 0.05 as a decimal.
For his new rate his original rate was multiplied by 1.05 ( original + 5%)
To find original amount, divide new amount by 1.05:
252 / 1.05 = 240
His original pay was £240
You can check by multiplying the original pay by 5% and adding:
240 x 0.05 = 12
240 + 12 = 252