A solution has 140 grams of KOH dissovled in 5 L of water. What is the pH ?

mols KOH = grams/molar mass

M KOH = mols/L solution
M (OH^-) = mols KOH since the KIOH is 100% ionized.
pOH = -log(OH^-)
Then pH + pOH = pKw = 14. You know pKw and pOH, solve for pH.