Mr thomas is buying two types of gift cards to give to employees at a company meeting. he will buy restaurant gift cards that each coast $50 . he will also buy movie theater gift cards that each coast $20. he has $450 to buy a total of 15 gift cards. how many of each type of gift card can mr this buy ?

To get this answer basically you have to play with the numbers, till you find ones that match. It may get irritating but if you keep trying you'll eventually find the right ones. 
So...
If he is only able to purchase $450.00 worth of gift cards, and a total of 15,
begin by. 

Doing simple math. 
Take 
$50.00 * 5 (You know he can purchase one 50 card for sure because of the $50. in $450
$50.00 * 5 = $250.00
Next take 15-5 = 10 (Amount of gift cards left to purchase)
Finally Take $20 * 10 = $200

When you add your restaurant give card and movie gift card amount you will receive the answer of $450.00 (to double check your answer)

When you add 5 + 10 you will receive the answer of 15 (to check the amount he has to purchase)

The correct answer would be 
Mr. Thomas can purchase a total of 5 restaurant gift cards and 10 movie gift cards to give to his employees.