Hello there!
So, remember that m = the slope, and slope intercept form is represented as y = mx + b. To find the y intercept, place the values of x, y, and the slope into the equation.
The first step, ____ = (____)____ + b should look like 3 = (2/5)10 + b once you plug the values for your x and y values and slope.
The second step, ___ = ____ + b should look like 3 = 4 + b since you should multiply 2/5 x 10.
The final step, -1 = b should look like since you subtracted 4 from both sides of the equation.
Y = 2/5x - 1 is your final equation. I hope this helps, have a great rest of your day!