I really need help on this question, a explanation also with details would be very appreciated. Please don't respond to my question if your not gonna say anything useful to me.

If you are trying to move an attached term across the equal sign (=), what operation would you use to move it?

What is the value of x when x + 7 = 21?

Sundar used linear combination to solve the system of equations shown. he did so by multiplying the first equation by 5 and the second equation by another number to eliminate the y-terms. what number did sundar multiply the second equation by? 2x+9y=41 3x+5y=36