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Triangle ABC and triangle DCE are congruent, so line DE = line AB
Use the cosine rule to find angle ACB






Angle ACB = 48.1°
The life span would be 24 months.
The formula for z-scores is:

Using the information we're given we have:

Multiply both sides by 8 to cancel it:
-3(8) = ((X-48)/8)*8
-24 = X-48
Add 48 to both sides:
-24+48 = X-48+48
24=X