we are given
Takuya's parents gave him $100
so,
total money =$100
he spent $20 out of his present on board games at the end of each month
It means that
money spent in 1 month is $20
Let's assume he takes 'x' months
so, total money spent = money spent in 1 month* total number of months
so, we get
total money spent =
total money spent =
now, we can set it to 100
now, we can solve for x
divide both sides by 20

so, total number of months is 5 .............Answer