Add (-2X) to both sides:
2X + B + (-2X) = C + (-2X)
If we (rearrange) it into B + 2X + (-2X) = C + (-2X)
B + 2X - 2X = C + (-2X)
Since +2X - 2X = 0
B + 0 = C + (-2X)
B = C + (-2X)
B = C - 2X
Because it’s a square garden each side is the same meaning 84/4 will give you the length of each side, in this case 21. to work out the area it is length x width so 21 x 21 is 441!
Use exponent rule: x^y * x^z = x^y+z
4^2 * 4^8
4^2+8
4^10
1,048,576
Best of Luck!