1 mole of [tex]{ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }[/tex] is 180 grams. (Molar mass).
18 is [tex]\frac { 1 }{ 10 } [/tex] of 180 , so it means 18 grams of [tex]{ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }[/tex] is [tex]\frac { 1 }{ 10 } [/tex] moles
To find a molecule's molar mass, you should multiply each atom's number with their atomic mass, in the molecule and add them I mean, there are 6 Carbon atoms, 12 Hydrogen atoms and 6 Oxygen atoms. So,
Atomic mass of Carbon is approximately, 12 amu (atomic mass unit), Hydrogen's is approximately, 1 and Oxygen's is approximately, 16. So :
[tex]{ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }\\ \\ C\quad \cong \quad 12\quad amu\\ H\quad \cong \quad 1\quad amu\\ O\quad \cong \quad 16\quad amu\\ \\ (6\cdot 12)+(12\cdot 1)+(6\cdot 16)\\ \\ 72+12+96=180\quad amu\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \quad \\ This\quad is\quad the\quad \\ glucose\quad molecule's\\ molar\quad mass\\ \\ [/tex]