When you isolate the variable, what must you do to keep the equation balanced x-3=7?

Hi, can anyone show me how to do this problem? 100 points for this. in advance

Mrs. avila is buying a wallpaper border to go on all of her kitchen walls. she wants to buy 5 extra feet of wallpaper border than she needs to be sure she has enough. she buys 55.5 feet of the border. the store owner selling the border uses the width of mrs. avila's kitchen to determine that the length of her kitchen must be 14.5 feet.

X^2/100+y^2/25=1 the length of the major axis is: a)5 b)10 c)20