Changing the size of an image used in a hyperlink XHTML

In an assignment i have to make a website with hyperlinks to external websites, the website has the styles in the head not on a separate css. I have a piece of of code that sets all the image size but the ones in the in the hyper links. how would i be able to change the size without having to change it for each individual hyperlink.

example of my hyperlink and my style for images

http://ift.tt/wJmNpX>http://ift.tt/1yB7tdz alt=boondock saints poster> img {width:178px;height:270px }