Question 669696
Let ch=chem, m=math, c=ceramics

therefore, ch=c+20 and m=2(c+20)
and thus ch+m+c= 2(c+20) + c+20 + c
                      180= 3(c+20) + c
                      180= 3c + 60 + c
                      180= 4c + 60
              180 - 60= 4c
                        60= 4c
                    60/4= c
and therefore c= $15

since we have found c we can then find ch and m:
ch=c + 20
    =15 + 20
    =$35

and

m= 2(c + 20)
   = 2(15 + 20)
   = 2 x 35
   = $70