457=(5.75*U+6.75*2.9)*30 simplify inside the parentheses
457 = ( 5.75 U + 19.575 ) *30 distribute the 30 across the terms in the parentheses
457 = 172.5 U + 587.25 subtract 587.25 from both sides
-130.25 = 172.5 U divide both sides by 172.5
- 0.755 = U ≈ -0.76
