Suppose strontium-90 decays at a rate of 2 percent per year. (a) Write the fraction PP of strontium remaining, as function of tt, measured in years. (Assume that at time t=0t=0 there is 100 % remaining.) P(t)=P(t)=equation editorEquation Editor (b) Estimate the half-life of strontium. equation editorEquation Editor Hint: Use your graphing calculator and the trace function. (Or use natural logarithms as in 1.9). (c) If presently there is 6.5 grams of strontium, estimate how many grams of the substance will remain after 22 years.