Solve[{z*14/138+y*14/115+a*28/80==20, y*31/115==4, x*39/74.55=30, z*40/138==20, t*24/246==5},{x,y,z,t,a}]

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.