Okay let me explain to you how this works. So let's take Belinda's intial sum of money to be x and wanil's initial sum of money to be y. From the question we know that Belina has 3 times the amount of money as wanil. So we can express that by the following equation:

X = 3Y - Equation 1

Next, after the 8 dollars deducted from Wanil, Belinda has 5 times the amount that Wanil has. That can be expressed in the following equation.

5(Y-8) = X - Equation 2

where y is the initial amount Wanil had.
And (y-8) is the amount Wanil was left with at the end.

5 x (y-8) = x is because Belinda had five times the amount of money that Wanil had at the end.

Next, substitute X = 3Y from equation 1 into equation 2

5(y-8) = 3y
5y-40 = 3y
2y = 40
Y = 20 (Wanil initially had $20)

Substitute y = 20 into equation 1

X = 3 x 20
= 60 (Belinda had $60)

Model method. I had uploaded a similar question with video presentation on YouTube “ ezmath/primary/model (basic) #4 “ you can learn from there to improve your maths.