Question 959015
{{{a[0]+d=-2}}}
{{{a[0]+2d=-7}}}
Subtracting,
{{{a[0]+2d-a[0]+d=-7-(-2)}}}
{{{d=-5}}}
Then,
{{{a[0]-5=-2}}}
{{{a[0]=3}}}
So,
{{{a[31]=3+31(-5)}}}
{{{a[31]=3-155}}}
{{{a[31]=-152}}}