The equation to obtain is

x2 - 5x - 16250 = 0

if you have done everything correctly.

To solve this by factorisation (the quadratic formula method is only covered in Sec 3 E Maths), it’s not easy.

The trick is, because I see a negative sign in front of the 16250, one number has to be positive and one number has to be negative (since the product of a positive number and a negative number is a negative number).

The two numbers chosen must be close to each other since their difference is the coefficient of x, -5.

This means that we must choose two numbers which are very close to each other and which multiply to 16250.

I tried my luck by square rooting 16250 since the two numbers must be clearly 100+ for the difference to be 5.

Square rooting 16250 gives 127+ which means that the two numbers must be very close to 127 (+ - 5), so I tried my luck with 125 and yes, the other number is 130.

The rest is just determining where the + and - signs go to.