a)

When we transform a quote into reported speech, we backshift tenses:

Present simple → Past simple 

Present continuous → Past continuous

Present perfect → Past perfect

Past simple → Past perfect

Past continuous → Past perfect continuous

Past perfect → Past perfect (no change)

Future simple → Future in the past (would + infinitive)

We also change pronouns, so that they refer to the speaker or the person they're talking to, from the perspective of a third person.

In Polish we change the pronouns, but backshifting tenses is optional.

(Kiedy przekształcamy bezpośrednią wypowiedź w mowę zależną, cofamy czas "o 1 do tyłu". Zmieniamy również zaimki, tak aby odnosiły się do osoby mówiącej lub jej rozmówcy, z perspektywy osoby trzeciej. W języku polskim zamieniamy zaimki, ale cofanie czasów jest opcjonalne.)

 

b) 

'The only time I feel alive is when I'm painting.' - Vincent van Gogh said that the only time he felt alive was when he was painting.

'It took me four years to paint like Raphael, but a lifetime to paint like a child.' - Pablo Picasso said that it had taken him years to paint like Raphael, but a lifetime to paint like a child.

'It has bothered me all my life that I don't paint like everybody else.' - Henri Matisse said that it had bothered him all his life that he didn't paint like everybody else.