Can anyone help with this problem?

Would appreciate any partial or full input. Thanks.

Suppose that we estimate a model:

but the true model is

What will the consequences be for our regression estimates? Are these serious; is this something we have to care about? Assume instead that it is the way around; thus, that the true model is.

but we are estimating

what are the consequences on our regression estimates. Are these serious consequences; do we need to care about this?

** Note:** No calculations are needed!