Your verbal translation is ambiguous. It could mean what you have written symbolically, but it could also mean multiply -3 times 2x and then add -4 to the product. To make it clear, I would phrase it thus:
"The product of negative three and the quantity consisting of the product of two and a number, said product reduced by four."
John
Egw to Beta kai to Sigma
My calculator said it, I believe it, that settles it