For a typically large organization how many dns servers should you install

How do we use the sumif formula (when dealing with different formats) ?

Cloud computing service providers manage different computing resources based on the services they offer. which resources do iaas and paas providers not manage? iaas providers do not manage the for the client, whereas paas providers usually do not manage the for their clients. iaas- storage server operating system network paas- applications interafce storage vertualiation

Need getting google account back, big issue