It’s easy, if the PH of any acidic solution = -Log[H+], where [H+] is hydrogen ion concentration, multiply each term by (-1) then raise each term as a power to (10), so it will become like this:-
[H+] = 10^(-PH)
Hey! i tried to work out the question in the clearest way I could. i hope this helps!! feel free to follow up if you have any more questions!!