This answer balances the equation by equating (the conservation of) the number of boron atoms on both sides of the equation.
H3BO3 and H4B6O11 are the only two boron-containing species in this reaction. Each molecule of H3BO3 contains one boron B atom whereas each molecule of H4B6O11 contains six. Add the coefficient 6 to the front of H3BO3 and 1 to H4B6O11 balance the number of boron atoms on the two sides.
6lH3BO3 → 1lH4B6O11+H2O NOT BALANCED
The left-hand side of the equation contains 6×3=18 oxygen O atoms. The number of oxygen atoms shall also conserve in this equation. Therefore H4B6O11 and H2O on the product side shall contain a total of 18 oxygen atoms. 11 of them go to the H4B6O11 molecule. Water molecules would account for rest 7 oxygen atoms.
Each water molecule contains one single oxygen atom. 7 of the oxygen atoms would thus correspond to 7 water molecules on the product side. Hence the equation:
6lH3BO3 → 1lH4B6O11+7lH2O
Optionally, check if the number of hydrogen H atoms on the two sides conserves to see if the equation is properly balanced:
- Number of H atoms on the right-hand side: 6×3=18
- Number of H atoms on the left-hand side: 1×4+7×2=18
The two numbers are equal, and thus this chemical equation is stoichiometrically balanced.
6lH3BO3 → 1lH4B6O11+7lH2O Balanced
Reference
"Balance Chemical Equation - Online Balancer," webqc.org,
https://www.webqc.org/balance.php, "Enter H3BO3 = H4B6O11 + H2O for this equation."