Convert 1/2-20 3a fractions into decimal

I need to convert the fraction at the beginning of a cells text into the decimal equivelent. for example 1/4-20 3A would give .2500.

I have this formula so far that works perfect for fractions that only contain 1 number on each side of the division sign such as 1/2.

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However if you type in 7/16-20-3A it gives an error. I can change the number in red to 4 or 5 and it will then work for 7/16 or 15/16, But then 1/2 will return an error.

So is there a way to write it so that it will work for ALL fractions up to 2 digits on each side of the division sign, such as 15/16?

Thanks for your time,

Adapated yours

=VALUE("0 "&LEFT(B11,FIND("-",B11)-1))

Assumes all strings contain a valid fraction and are followed by a hyphen.