Answer:
-3.1
Step-by-step explanation:
[tex]a=-1/4=-0.25\\\\-0.5(3a+4)+1.9a-1=\\\\-0.5(3*-0.25+4)+1.9*(-0.25)-1=\\-0.5(-0.75+4)+1.9*(-0.25)-1=\\-0.5(3.25)+1.9*(-0.25)-1=\\-1.625+1.9*(-0.25)-1=\\-1.625-0.475-1=\\-2.1-1=\\-3.1[/tex]