Simplify the expression by combining like terms. 15+12−5+4−7

Ijust need to see how to do this. so you don’t have to answer all of them just a step by step explanation of one.

Ascientist has discovered an organism that produces five offspring exactly one hour after its own birth, and then goes on to live for one week without producing any additional offspring. each replicated organism also replicates at the same rate. at hour one, there is one organism. at hour two, there are five more organisms. how many total organisms are there at hour seven? 2,801 19,531 19,607 97.655

Suppose 38 lbs of coffee beans are required to produce 2 lbs of farmer's coffee. how many lbs of coffee beans are required to produce 309 lbs of farmer's coffee?