How do you solve 5y-1/2=7?

You wrote:
5y -1/2 = 7 according to PEMDAS
add 1/2
5y = 7 + 1/2
5y = 14/2 + 1/2
5y = 15/2
divide by 5
y = 3/2
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IF you meant (5y - 1)/2 = 7 that is a totally different problem.
Much like commas, parens are very important:
Let's eat grandpa! vs Let's eat, grandpa!
(5y - 1)/2 = 7
multiply by 2
5y -1 = 14
add 1
5y = 15
divide by 5
y = 3.
So you meant to write (5y - 1)/2 = 7

Your problem is POORLY presented...perhaps you are not interpreting it correctly !!

(5y - 1)/2 = 7

clear the denominator...multiply both sides by (2)

5y - 1 = 14

add (1) to both sides...

5y = 15

solve...

y = 3

Show your work to learn your mistake(s) !

(5y - 1)/2 = 7
5y - 1 = 14
5y = 15
y = 3

First Step
ADD 1/2 to each side of the equation
Results:
5Y = 7.5
Next step > Divide both sides by 5
Results
Y = 1.5

There is no way Y could equal 3 unless you wrote the equation incorrectly. Like leaving out the brackets
(5y-1)/2 =7 would come out with y=3