book Maths Puzzle Numerical Ability

How old is a skeleton that has lost 75% of its Carbon-14? I have NO idea how to do this problem. Could someone help me?

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there are two solutions for the equation {{{bx^2-cx+a^2=0}}} (where a,b,and c are constants, and x is the unknown). They differ by the sign of the square root. Enter the the on wit Bob sold hammers and wrenches at a flea market. He sold 4 times as many hammers as wrenches. The total sales equaled $609.00. If the hammers sold for $3.00 apiece and the wrenches for $2.50 each how many hammers and wrenches did he sell?