I have just finished a self-test with this question, but do not understand the answer.

They give the following regression equation:

sales = 10.2 + (5.6 x DOL) + (6.3 x IP) + (9.2 x GDP)

SEE for DOL 5.4, IP 4.2 and GDP 5.3

They state the hypothesis: A 2 % increase in DOL will result in an increase in sales of more than 12 %.

If I understand this correct it is a one-tailed t-test because they are asking for > 12 %? But, I do not understand why the t-statistic is (5.6 - 6)/3.5 = -0.114

They state: The 12 % increase will only happen if the value of the coefficient is greater than 6, since 2x6 = 12. Could someone explain this in another way maybe?