Find the number of homes with 3000 sq ft , 3 number of bedrooms and 40 years of age?
If it's &quot;find the house&quot; then that implies that you need to find the house with those specific attributes in the dataset. I'm not sure what programming language you're using but it should be pretty simple to do such a thing anyways.
If it's &quot;find the price of a house with...&quot; that implies there probably isn't such a house in the dataset and you need to train a predictive model to predict the price of such a house. You said to use linear regression, which is a fine choice, if your data is linear... But I would instead suggest an SVR (Support Vector Machine Regressor), and fine-tune some things like the kernel and regularization.