Please can u help? 10 pts best answer?

i feel REALLY dumb asking this, especially since i'm in the smartest cl, but i don't get fractions AT ALL! In one question it says When Mrs Brier does her weekly shopping she spends $135, which is 3 over 8 of hr weekly budget. How much money does she have left to spend elsewhere!! I DON'T UNDERSTAND A THING unless she has 135...........please help me...I have a HUGE test tomorrow on all my subjects, but im struggling with maths :'(.............please can you explain how fractions work e.g 2 over 5, 6 over 8, 9 over 5 or whatever ( they're just examples!! ) PLEASE AND THANK U SOOOOOOOOOOO MUCH WHOEVER ANSWERS THIS....U HAVE NO IDEA WHAT IT MEANS TO ME AND U'LL RECIEVE 10 PTS...I PRMOISE!! THANK UU bella XXXXXX