Please help me with all subquestions.

3. Suppose consumers value a high-quality used cellphones at $400 and a low-quality used cellphones at $100. The supply of high-quality cellphones is QH = PH - 100 The supply of low-quality cellphones is Q1 = 2PL - 50 Buyers cannot tell the difference between the cellphones a. If buyers believe that 0.75 of cellphones are high-quality, what price would they be willing to pay for a cellphone? b. At the price above, how many high-quality cellphones will be available? How many low- quality cellphones are available? Are 75% of cellphones high-quality