Answer:
456.083
Explanation:
Use basic algebra to solve this problem:
0.217 + x = 456.3 (x just means an unknown value)
Subtract 0.217 from both sides. When you do this, it cancels out on the left side. REMEMBER: whatever you do to one side, you MUST do it to the other.
0.217 - 0.217 + x = 456.3 - 0.217
x = 456.083
0.217 + 456.083 = 456.3
Hope that helps