The tangent to the curve y=ax˛+bx at the point where x=1 has a gradient 1 and passes through point (4,5). Find a and b. Question is frustrating me .

Here's what I've got.

dy/dx = 2ax+b

(For x=1) 2a+b=1

Using curve and other given point: 5=16a+4b

Now when I put these into a sim eqation and solve it's wrong :/ I have no idea why either.