Solved! i am having a 2× 15w speaker and 1×35 w sub woofer which amp should i buy amp less than 50w

You need a 2.1 channel amplifier with power ratings to match the speakers.
Most of these mini amps will have wildly exaggerated power specs so you have to dig into the description. The power rating should be at the same impedance of the speaker. The distortion should be at .1% or lower.
Something like this
https://www.amazon.com/Yeeco-Channel-Stereo-Amplifier-Subwoofer/dp/B072Q8GTXJ
 
Solution