Can someone solve those exercises? I'll be really grateful for explanation too. If you can't solve, just please tell me step by step how can I do it by myself

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.

explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length