Explanation:
so, write that down mathematically :
7 - k×43 = k
to bring k to only one side of the equation we add e.g. 43k to both sides (it is important to perform any operation on an equation always on both sides, otherwise the equality relation is destroyed)
7 - 43k + 43k = k + 43k
7 = 44k
k = 7/44