You can use 了 twice in a sentence to show that someone has been doing something for some time. Just say 了 after the verb, and then again after the amount of time.
我工作了十个小时了。
Wǒ gōngzuò le shí ge xiǎoshí le.
I’ve been working for ten hours.
If the verb has an object (like 跑步 or 学中文), repeat the verb again before adding 了.
他们学中文学了两年了。
Tāmen xué Zhōngwén xué le liǎng nián le.
They have been learning Chinese for two years.
我等你等了很久了。
Wǒ déng nǐ děng le hén jiǔ le.
I have been waiting for you for a long time.
她跑步跑了二十分钟了。
Tā pǎobù pǎo le èrshí fēnzhōng le.
She has been running for twenty minutes.
To say that something is even more difficult, even harder, or even better, add 更 before the adjective .
我觉得写汉字更难。
Wǒ juéde xiě Hànzì gèng nán.
I think writing Chinese characters is even more difficult.
明天会更好。
Míngtiān huì gèng hǎo.
Tomorrow will be even better.
我会更努力学习中文。
Wǒ huì gèng nǔlì xuéxí Zhōngwén.
I will study Chinese even harder.