x - number of pens
y - number of stickers
{x + y = 5,000
{0.23x + 0.14y = 970
{x = 5,000 - y
{0.23(5,000 - y) + 0.14y = 970
{x = 5,000 - y
{1,150 - 0.23y + 0.14y = 970
{x = 5,000 - y
{-0.09y = -180
{x = 5,000 - y
{y = 2,000
{y = 2,000
{x = 3,000
He gave away 3,000 pens.