Exponent graph thing

Pleaseeee someone help me with this question I’ve tried so many times and can’t seem to get the hang of it

The diagram shows a sketch of the graph with equation y = ab^-x

P(3, 0.75)
*
P is a point on the graph with coordinates (3, 0.75)
Work out the value of a and the value of b.

It would help to see the graph, so what is the value when x=0 and what does that tell you about "a". Then use the given point P to infer the value of "b" which I guess can be done without a calculator.

Can it really be done in that way? I would get y = a for x = 0. Don't see how this helps, as the point P has a different x value.

Im presuming/guessing the graph has the axis crossing point marked on. As the OP didnt post it, its probably
https://p16-ehi-va.gauthmath.com/tos-maliva-i-ejcjvp0zxf-us/7adf912d3ff241159e0adff3f9196276~tplv-ejcjvp0zxf-webp-scale:746:851.webp