Question 324805
Let A be the amount of acid, B the amount of water.
{{{A+B=210}}}
{{{B=A+120}}}
Substitute eq. 2 into eq. 1,
{{{A+A+120=210}}}
{{{2A=90}}}
{{{highlight(A=45)}}}
Then
{{{B=45+120}}}
{{{highlight(B=165)}}}