I need to solve these problems and know how to solve them . Thank you.

1. How many different 7- place license plates are possible if the first 3 places are to be occupied by letters and the final 4 by number: a- If repetition is allowed to both letters and numbers. b- If repetition is not allowed to both letters and numbers. c- If repetition is allowed to numbers only. d- If repetition is allowed to letters only. 2. From a collection of 7 different numbers and 8 different letters, 7 - place license plates can be designed in such a way that the first 4 places are numbers and the next 3 places are letters. Determine the number of possible designated plates, if repetition is allowed for numbers only. 3. From a collection of 6 different numbers and 8 different letters, 11-place license plates can be designed in such a way that the first 4 places are numbers and the next 7 places are letters. Determine the number of possible designated plates, if repetition is allowed for both numbers and letters. 4. Zip Codes How many 5-digit zip codes are possible if digits can be repeated? If there cannot be repetitions? 5. Identification Tags How many different 3-digit identification tags can be made if the digits can be used more than once? If the first digit must be a 5 and repetitions are not permitted? 6. Sports Car Stripes How many different 4-color code stripes can be made on a sports car if each code consists of the colors green, red, blue, and white? All colors are used only once. 7. ID Cards How many different ID cards can be made if there are 6 digits on a card and no digit can be used more than once