Or cover up the 5d with your finger.
Something take 11= 3
So the something under your finger must be 14 because you know 14-3=11.
So 5d= 14
So 1d (written just as d) is 14 divided by 5
Maybe your son (?) needs to go back a step.
Does your son realise what 5d means? In your later post you indicated it may mean 5+d. which is wrong. And does he know that d is a shorthand way of saying 1d?