HELPPPPPPPPPPPP PLEASEEEEWESSSSEE AND EXPLAIN HOW TO DO THIS BECAUSE I FORGOT HOW SO I CAN REALLY USE A HELP ON HOW TO DO THESE TYPE OF MATH EQUATION SO PLEASE HELP

Answer:
5.7
Step-by-step explanation:
They give you the value of a. Take that value and plug it into the equation.
2a + 3.1
a = 1.3
2(1.3) + 3.1
2.6 + 3.1
5.7
Hope this helped!