Chapter 4 - Section 4.3 - Quadratic Functions and Their Properties - 4.3 Assess Your Understanding - Page 301: 87

See below.

Let's compare $f(x)=x^2-140x+7400$ to $f(x)=ax^2+bx+c$. We can see that a=1, b=-140, c=7400. a>0, hence the graph opens up, hence its vertex is a minimum. The minimum value is at $x=-\frac{b}{2a}=-\frac{-140}{2\cdot 1}=70.$ Hence the minimum value is $f(70)=(70)^2-140(70)+7400=2500.$ Thus: a) $70000$ b)$2500$