Left align an equation without changing alignment of its content

[jakobkmar]

Example

Given the following equation:

#let myeq = $
4x^3 + 3x^3 + 2x^2 + 1x + 3 &= 0 \
a &= 3b
$

I know about two ways to left-align this equation:

First:

#align(left, math.equation(myeq))

Second:

#show math.equation: block
#myeq

Both work for left-aligning the equation, but in both cases the internal alignment changes.

Images

In this particular example, this means that the a wont be next to the equals sign anymore:

It renders as this:

But I want this:

Question

How can I change this, so that the normal alignment (second image) will be kept in tact, even when left-aligning the equation as a whole?