Compare and if true do a calculation

Hi, I’m trying to compare the content of a wappler variable (on a form change) to see if it matches a text string - if it does, I want to run a calculation. (if then)

I’m having a problem and not sure if what I’m trying to do is impossible or if I just have a syntax error. Code section below…

<input type="number" class="form-control" id="pizzasize" name="pizzasize" placeholder="Enter Pizza Size in Inches" value="5" data-rule-min="5" data-rule-max="30" dmx-bind:disabled="input1_group.input1_2.checked" dmx-bind:value="form1.pizzasizesq.value" dmx-on:change="var1wordsforcalculatebydropdown.value == &quot;Thickness Factor&quot; ? OnceGramValue.setValue((((28.3495 * tf.value * (((3.14159265359 * (pizzasize.value / 2).pow(2))) * 1)).round(2))))">