9a-3d=31

-3d+1d=-1

Solve by elimination

a = 65/18, d = 1/2

Step-by-step explanation by elimination:

Solve the following system:

{9 a - 3 d = 31 | (equation 1)

-2 d = - 1 | (equation 2)

Multiply equation 2 by - 1:

{9 a - 3 d = 31 | (equation 1)

0 a+2 d = 1 | (equation 2)

Divide equation 2 by 2:

{9 a - 3 d = 31 | (equation 1)

0 a+d = 1/2 | (equation 2)

Add 3 * (equation 2) to equation 1:

{9 a+0 d = 65/2 | (equation 1)

0 a+d = 1/2 | (equation 2)

Divide equation 1 by 9:

{a+0 d = 65/18 | (equation 1)

0 a+d = 1/2 | (equation 2)

Collect results:

Answer: {a = 65/18, d = 1/2