Answer is: volume of the acid is 0,075 L.
Chemical reaction: KOH + HCl → KCl + H₂O.
V(KOH) = 30 mL · 0,001 L/mL = 0,3 L.
c(KOH) = 0,5 M = 0,5 mol/L.
c(HCl) = 2 M = 2 mol/L.
V(HCl) = ?
From chemical reaction n(KOH) : n(HCl) = 1 : 1.
n(KOH) = n(HCl).
c(KOH) · V(KOH) = c(HCl) · V(HCl).
0,5M · 0,3 L = 2M · V(HCl).
V(HCl) = 0,075 L.