The oxygen equivalence number of a weld is a number that can be used to predict properties such as hardness, strength, and ductility. The article “Advances in Oxygen Equivalence Equations for Predicting the Properties of Titanium Welds presents several equations for computing the oxygen equivalence number of a weld. An equation designed to predict the strength of a weld is X=1.12C+2.69N+O–0.21 Fe, where X is the oxygen equivalence, and C, N, O, and Fe are the amounts of carbon, nitrogen, oxygen, and iron, respectively, in weight percent, in the weld. Suppose that for welds of a certain type, 
, 
Furthermore assume that correlations
are given by 
a. Find 
.
b. Find Cov(C,N), Cov(C, O), Cov(C, Fe),Cov(N, O), Cov(N, Fe), and Cov(O, Fe).
c. Find 
.
(a)
(b)
(c)
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