If you are to solve for x in the congruence $\displaystyle 7x=20(mod50)$

What is the easier way to do it without using a calculator or any other type of electronic device. I know you can add 7 to 20 until the number is divisible by 7 and then divide by 7 to reduce it to a solution but that takes a while. I need to figure out how to get it done in just a minute or two. Thanks.