Please help me with this!

a) Everything else held constant, what will happen to the equilibrium price and quantity of pens if the following events occur simultaneously - price of pencils rises and the union of pen-makers negotiate for a higher wage? Provide brief explanation. (2.5 marks) b) Everything else held constant, a 4 percent increase in the price of a pen causes a 3 percent decrease in quantity demanded for the same. Calculate the price elasticity of demand for a pen. (1 mark) c) In this case, explain briefly whether the revenue will increase or decrease? (1.5 marks)