Which elements together make up seven percent of the earths crust? calcium and iron calcium and sodium potassium and magnesium potassium and sodium

The earth's crust comprises a number of chemical elements. Here are a few along with the abundance as a percentage: Iron 5.63% Calcium 4.15% Sodium 2.36% Magnesium 2.33% Potassium 2.09% When asked which two elements make up seven percent of the earth's crust, we must find which two numbers (of the combinations listed) sum to 7. The closest sum is calcium and sodium, whose percentages sum to 6.51%.