How do I ifft two vectors?

This is the question:

Use fft() and ifft() functions provided by MATLAB, while X[k] = fft(x[n]).Compute the result for the following equations and plot the result. Describe your findings.

i)H1[k] =fft(h[n]), y[n] =ifft(X[k]H1[k])

ii)H2[k] =fft(h[n+ 12] +h[n] +h[n−12]), y[n] =ifft(X[k]H2[k])

iii)H3[k] =fft(h[n+ 5] +h[n] +h[n−5]), y[n] =ifft(X[k]H3[k])

How do I find y[n] in each of these, I have tried

ifft( (X[k])*(H1[k]))

and

ifft( (X[k]).*(H1[k]))

, but I get the error message, "Arrays have incompatible sizes for this operation." So how do i make them the same length and then appy that to the ifft.

Thank you!

[Image Analyst]

What does x[n] mean? You can't fft a single value, so is x a 2-D array and x[n] is the nth row or column of that array? You use parentheses to reference array indices in MATLAB, not square brackets. Square brackets are for creating matrices, not referencing elements from them. If you're using the whole matrix, then maybe you meant:

ft = ifft(x .* h1)