well molarity is moles solute divided by liters solvent, and you know you want 20mL of solution at 1.0M, so it's just a matter of plugging it all into the formula.
1.0M=(x moles)/(0.02L), and you'll find that you need 0.2mol of the substance. the molar mass of the compound is 138.2g, so do a proportion of 138.2g/1mol = x g/.2mol, and cross multiply. you'll find that you need 27.64g of the substance. so just mix that amount in with 20mL of water and you should be set.
that should be right, double check for any errors.
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