Write the number equal to 2 tens 15 ones.

So first count to 10 (I hope this doesn't sound rude). If your done counting to 10 count ten more again (10 + 10 = 20). So now you have 20. There are 15 ones. Here's our number problem, 20 + 15. To do this any easier way add 5 to 20. Which is 25, then add 10 more which is 35. Or add 5 to 20 then add another 5 then another 5. But the answer is 35 :). If you try your hardest and try to make it in a way you can understand it, you will get good at it ( I hope that doesn't sound rude ^-^)!