Find a liner equation f(x) with slope 5 such that f(3)=12
Using f(x) the formula would be f(x) = 5x + b. The standard form of the slope intercept formula is
y = mx + b. The slope is represented by m, which equal 5. Since you know that f(3) = 12, the only unknown is b. So you simply plug in the known information and solve.
y = mx + b
12 = 5(3) + b
12 = 15 + b
Subtract 15 from both sides.
b = -3
Prove the formula.
12 = 5(3) - 3
12 = 15 - 3
12 = 12