Acertain bank balance b is given by b= 100+d-w where d is deposits and w is withdrawls. what is the balance when d =100 and w=125

You know that d = 100 and w = 125, so you plug that into the equation and solve as shown:
b= 100 + d - w
  = 100 + 100 - 125
  = 200 - 125
  = $75
You now have $75 left as balance.

So problem says that 100 is deposit and 125 is withdraw.

So you have equation b = 100 + d - w. You have given information d = 100 and w=125, so all you have to do is to plug in values. You replace d to 100 and w to 125.

b = 100 + d - w
b = 100 + (100) - (125)
b = 75

So when d = 100 and w=125, the balance would be 75.

Final 75

Hope this helps.