Question 19353
in these problems ,transfer all known to one side of the = sign ,usually rhs and all unknowns to the other side of = sgn ,usually lhs of = sign...while transferring from one side of = to the other + becomes - and - becomes +...now simplify both sides...now you will get finally (some number)*(unknown)=known value..now the unknown =known value/ (some number)..which was multiplying the unknown earlier on the lhs of = sign..SEE THE EXAMPLES BELOW..
1. 3/8 - 1/4t = 1/2t - 3/4
3/8+3/4=1/2t+1/4t...(consider t as some apple ..this means add 1/2 apple to 1/4 apple..we keep aside the apple and add the numbers )=t(1/2+1/4)=t((2+1)/4)
=t(3/4)...so we got 
t(3/4)=3/8+3/4=((3+2*3)/8=(3+6)/8=9/8
t(3/4)=9/8
t=(9/8)/(3/4)=(9*4)/(3*8)=3/2...
so t=3/2
you can verify the answer by substituting for t the value of 3/2 and check whether the equation is satisfied..we get ...
3/8-(1/4)*(3/2)=3/8-3/8=0 is the lhs of =
(1/2)*(3/2)-3/4=3/4-3/4=0 is the rhs of =..
so lhs = rhs ..so our answer is correct.

2. 20c + 5 = 5c + 65
20c-5c=65-5=60
15c=60
c=60/15=4
c=4...check the answer as before

3. 7 - 3r = r - 4(2+r)
7-3r=r-4*2-4*r
7-3r=r-8-4r
7+8=15=r-4r+3r=r(1-4+3)=r*0=0...THE PROBLEM DOES NOT HAVE A PROPER SOLUTION
SINCE LHS=15 and RHS=0..THEY CANNOT BE EQUAL