exam Maths Puzzle Numerical Ability

I am having trouble understanding how to distribute the negative number. Please explain.

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4x+5y=5
8x+10y=10
I need to solve this using elimination
* I know I need to solve for x and use that answer in the next equation, but not sure what one I have to start with. Your help is appreciated. how would I solve for f1 in an equation that is V=speed(f1-f0)/(f1+f0). what is the equation for f1