could you please show me how to do this step by step. 3+2x4/5=

I think you mean 3+2 * \frac{4}{5}

which is equlivelent to:

3+ \frac{2*4}{5}

Can you take it from there?

With computers the "*" is generally used to mean multiply.

Yes, you need to remember 'BODMAS' which is the acronym for: 'Brackets Of Division Multiplication Addition Subtraction'

You work out according to this order, that is you look for brackets first (work them out first), then you look for division, then for multiplication, then addition and last subtraction.

In your problem, the first which comes is multiplication, so, work out the multiplication first like galactus said.