When using straight ladders, the base of the ladder should be away from the wall or other vertical surface for every of height to the point of support.

Answer;

one foot; four feet

Explanation;When using straight ladders, the base of the ladder should be one foot away from the wall or other vertical surface for every four feet of height to the point of support.The Four-to-one rule ladder safety requires that for every four feet of height climbed, move the base one foot away from the wall.It is always important to remember the 4-to-1 rule for ladder safety so as to avoid home improvement injuries.

Depending on how the continental plates move it can cause a continental scale shift.