Answer:
Geometrically, ca is an extension or contraction of a, and algebraically is a multiplication of c times every coordinate of a.
Explanation:
A vector is an element of a vectorial space which could have n-coordinates (or dimensions). A scalar is just a number (they don't specify if it is real, complex, rational, etc.).
In order to find ca (or c*a), we have that, in general
is the vector a, and ca is c times the vector a
Geometrically, this represents an extension or contraction of the vector a.