How to do linear equations 27, 28,28,30

#27.  
First cross multiply
2 (2a-3) = 3 (a-1)
next use the distribute property on both sides
4a - 6 = 3a - 3
combine like terms, subtract 3a from both sides and add 6 to both sides
a = 3

#28
cross multiply
3x = 4, then divide both sides by 3
x = 4/3

#30
add 1/4 to both sides
3/x = 1/2 + 1/4, find a common denominator for the right side fractions
3/x = 2/4 + 1/4 = 3/4
therefore, x = 4