First subtract the 2 to isolate the 7x. Remember what you do to one side you do to the other, so then you would subtract 2 from 30 as well giving you 7x=28. After that in order to isolate x, you would divide by 7 on both sides giving you x=4.
answer is about once a year
Nikola Tesla was an inventor in the old days and he was also an engineer too.