The addition of a gratuitous promise to the acceptance does not render it inoperative as an acceptance.1 If A offers to do certain work for B, B's acceptance is not rendered invalid by the fact that B promises to employ A to do certain other work.2 An acceptance by a contractor of an offer by a subcontractor to lay the surface on a specified street for a specified amount, is not rendered inoperative by the fact that in the letter of acceptance the contractor promises to let the contract to another street to such subcontractor if the contract therefor is awarded to such subcontractor.3