Add echo to audio recording

Write a function output = echo_gen(input, fs, delay, gain); Where input is a column vector, fs is sampling rate, delay is delay and gain is the gain of the echo, which is less than 1. The output vector will be longer than the input vector if the delay is not zero (round to the nearest number of points needed to get the delay, as opposed to floor or ceil). A sound recording has values between -1 and 1, so if the echo causes some values to be outside of this range, you will need to normalize the entire vector, so that all values adhere to this requirement. I have no idea how to approach this, as I have only ever worked with basic matrices as opposed to actual signals in MATLAB.