Here's a simple algebra problem than can be solved INSTANTLY with first semester calculus:
What are the dimensions of a rectangular area that can be fenced with 32 feet of fabric having the maximum possible area.
One side is x, the other is 16-x so when you add two of each side, the x's drop out and you have 32 feet of fence - what you started with.
From first semester calculus, we're going to find the vertex of the area curve and the area is x * (16-x) or 16x - x^2. Differentiate the expression to find the point where the slope is zero (the peak) and you wind up with 2x = 16 or x = 8. So, the maximum area is 8 x 8 or 64 square feet. In the algebra class they solved the problem by creating a table of values and looking for the maximum. But they didn't know, nor could they prove, that they had found the absolute maximum. But calculus does prove it. The vertex of a parabola is a point and it occurs exactly where the slope is 0.
So, yes, calculus is important! For engineers, of any kind, math is everything. Engineering is math!