c over d means c/d it is another way of saying "divided by"
4cd over 2c is actually 4cd/ 2c
this can be simplified as 2d (since 2c will be cancelled from both denominator and numerator)
SO the value of 4cd/2c = 2d =2*2 = 4
Value of 2cd over 2c = 2cd/ 2c = d =2
Hope this helps.