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Which is an equation for the nth terms of the sequence 12,15,18,21

(a) calculate the molarity of a solution that contains 0.0345 mol nh4cl in 400 ml of solution. (b) how many moles of hno3 are present in 35.0 ml of a 2.20 m solution of nitric acid? (c) how many milliliters of 1.50 m koh solution are needed to supply 0.125 mil of koh ?

12x + 1 = 25 solve the following equation. then place the correct number in the box provided.