Determine the amount of the child tax credit in each of the following cases:

$\backslash$table$[[,\backslash$table$[[$Child Tax$],[$Credit$],[$Allowed$]]],[$a A single parent with modified AGI of $$214,500$ and one child age $4.,],[$b A single parent with modified AGI of $$79,100$ and three children ages $7,9$ and $12,],[$c$.$ A married couple, filing jointly, with modified AGI of $$409,033$ and two children age $14$ and $16,],[$d$.$ A married couple, filing jointly, with modified AGI of $$133,155$ and one child, age $+3,]]$