Answer(a):
Order of matrix A = 3x3 {because number of rows=3, number of columns=3}
Order of matrix B = 3x3
Order of matrix C = 1x3
3A will be of order 3x3 because multiply by scalar doesn't change the order. Which is same as the order of matrix B.
So 3A+B is possible.
We simply multiply all elements of A with 3 and add them with corresponding elements of B.

Answer(b):
2B will be of order 3x3 because multiply by scalar doesn't change the order. Which is NOT same as the order of matrix C.
So 2B+C is NOT possible.
Answer(c):
CA is possible only if
number of columns of C = number of columns of A
3=3
which is true hence CA is possible.

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<em><u>If the matrix is not visible properly then look at the attached picture.</u></em>